Recombinant DNA molecules and expression vectors for erythropoietin

ABSTRACT

A recombinant DNA molecule adapted for transfection of a host cell comprising a nucleic acid molecule encoding mammalian erythropoietin, an expression control sequence operatively linked thereto and at least one SAR element. The invention also relates to expression vectors having the recombinant DNA molecule and to mammalian cells transformed with the expression vector. The mammalian cells lack multiple copies of an amplified amplification gene and are capable of expressing recombinant EPO in vitro at levels of at least 1,500 u/10 6  cells in 24 hours. The invention further relates to a method of expressing recombinant mammalian erythropoietin using the expression vectors and to a transgenic non-human animal or embryo whose germ cells and somatic cells contain a DNA construct having the recombinant DNA molecule of the invention.

FIELD OF THE INVENTION

The invention relates to recombinant DNA molecules adapted for transfection of a host cell, and having a nucleic acid molecule encoding mammalian erythropoietin, operatively linked to an expression control sequence and having at least one SAR element. The invention also relates to expression vectors for transfection of a host cell and to host cells for expressing erythropoietin. The invention further relates to methods of preparing recombinant erythropoietin using the host cells transfected with the expression vectors.

BACKGROUND OF THE INVENTION

Erythropoietin (EPO) is a heavily glycosylated acidic glycoprotein with a molecular weight of approximately 35,000. The protein consists of 166 amino acids and has a leader signal sequence of 27 amino acids which is removed in vivo during secretion from the host cell. The sequence encoding the unprocessed EPO is 579 nucleotides in length (Jacobs et al, 1985, Lin et al, 1985, U.S. Pat. No. 4,703,008 and WO 86/03520).

Erythropoietin is the principal hormone involved in the regulation and maintenance of physiological levels of erythrocytes in mammalian circulation and functions to promote erythroid development, to initiate hemoglobin synthesis and to stimulate proliferation of immature erythroid precursors. The hormone is produced primarily by the adult kidney and foetal liver and is maintained in the circulation at concentrations of about 10-20 milliunits/ml of serum under normal physiological conditions. Elevated levels of EPO, induced by tissue hypoxia, trigger proliferation and differentiation of a population of receptive progenitor stem cells in the bone marrow, stimulating hemoglobin synthesis in maturing erythroid cells and accelerating the release of erythrocytes from the marrow into the circulation.

Recombinant EPO has been used to successfully treat patients, including patients having anemia as a result of chronic renal failure. As EPO is the primary regulator of red blood cell formation, it has applications in both the diagnosis and treatment of disorders of red blood cell production and has potential applications for treating a range of conditions.

The urine of severely anaemic patients was, at one time, almost the sole source for the commercial isolation of EPO. U.S. Pat. No. 3,033,753 describes a method for obtaining a crude EPO preparation from sheep plasma. The preparation of monoclonal antibodies specific for human EPO provided a means for identifying EPO produced from EPO mRNA, for screening libraries and for cloning the EPO gene. Human EPO cDNA has been cloned and expressed in E. coli (Lee-Huang, 1984, Proc. Natl. Acad. Sci. 81:2708). Isolation of the human EPO gene using mixtures of short or long synthetic nucleotides as probes led to the expression of biologically active EPO in mammalian cells (Lin, 1985, Proc. Natl. Acad. Sci. 82:7580; Lin, WO 85/02610; Jacobs, et al., 1985, Nature (Lond.) 313:806; Goto et al., 1988, Biotechnology 6:67). Jacobs, et al., 1985, supra, described the use of plasmids containing EPO DNA which were not integrated into the chromosomes of the COS host cells, but replicated autonomously in the cells to many thousands of copies, thereby killing the cells. Thus the expression of EPO was only a transient phenomenon in these cells.

Lin, in U.S. Pat. No. 4,703,008, reported expression of the human EPO gene in COS-1 and CHO cells. However, attempts to use transfected cells as production vehicles for EPO have been hampered by the low levels of EPO expressed by transfected cells. Given the important applications of recombinant EPO, there is much interest in developing more efficient methods for the expression of EPO.

Lin in U.S. Pat. No. 4,703,008 reported methods to increase the low amounts of EPO produced by transfected CHO cells (e.g. 2.99 u/ml/3 days) by a process of gene amplification. Levels of approximately 1500 units EPO/10⁶ cells/48 hours were reported by Lin, following amplification. Gene amplification involves culturing cells in appropriate media conditions to select cells resistant to a selective agent, such as the drug methotrexate. Selection for cells resistant to methotrexate produces cells containing greater numbers of DHFR genes and passenger genes, such as the EPO gene carried on the expression vector along with the DHFR gene or transfected with the DHFR gene.

However, gene amplification is a very time consuming and labour intensive process. A major disadvantage of amplification is the inherent instability of amplified genes (McDonald, 1990, Crit. Rev. Biotech. 10:155). As it is usually necessary to maintain the amplified cells in the presence of toxic analogs to maintain high copy number, amplification may be inappropriate for large scale production due to the costs and toxicity of the selective agent. The high copy number of the DHFR-target transgene may also sequestor transcription factor, leading to a retardation of cell growth.

Genomic clones of human EPO have been used in attempts to develop stably transfected mammalian cell lines that secrete high levels of active erythropoietin (Powell, et al., 1986, Proc. Natl. Acad. Sci. 83:6465; Masatsuga, et al., European Patent Application Publication No. 0 236 059). In PCT Application WO 88/00241 Powell, describes the preparation of mammalian cell lines (COS-7 and BHK) transfected with the Apa I restriction fragment of the human EPO gene and selected for high expression by amplification.

Human EPO cDNA has also been expressed in mammalian cells (Yanagi, et al., 1989, DNA 8:419). Berstein, in PCT application WO 86/03520 describes the expression of EPO cDNA in various host cells, resulting in the secretion of up to 160 ng/ml of EPO into the medium after amplification. European Patent Application publication No. 0 267 678 discloses expression of recombinant EPO and secretion into the culture medium at levels of 600 units/ml.

A few scaffold attachment region (SAR) elements have been shown to increase the expression of reporter genes in transfected cells. SAR elements are thought to be DNA sequences which mediate attachment of chromatin loops to the nuclear matrix or scaffold. SAR elements are also known as MAR (matrix-associated regions) (reviewed by Phi-Van and Stratling, Prog. Mol. Subcell. Biol. 11:1-11, 1990). These elements will hereinafter be referred to as "SAR elements". SAR elements are usually 300 or more base pairs long, and they require a redundancy of sequence information and contain multiple sites of protein-DNA interaction. SAR elements are found in non-coding regions: in flanking regions or introns.

Stief, et al., (Nature 341:343-345, 1989) stably transfected chicken macrophage cells by constructs which contained the CAT gene either fused to the lysozyme promoter, or to the lysozyme promoter and the lysozyme enhancer. When the transcription units contained in both constructs were flanked on both sides by lysozyme 5' SAR elements (A elements), gene expression was increased about 10 times relative to transfectants, which contained the constructs lacking the SAR elements.

Phi-Van, et al., (Mol. Cell. Biol., 10:2302-2307, 1990) determined the influence of the SAR element located 5' to the chicken lysozyme gene (A element) on the CAT gene expression from a heterologous promoter (herpes simplex virus thymidine kinase promoter) in stably transfected heterologous cells (rat fibroblasts). The median CAT activity per copy number in transfectants was 10 times higher for the transcriptional unit flanked on both sides by A elements than for the transcriptional unit lacking SAR elements.

Klehr, et al., (Biochemistry, 30:1264-1270, 1991) stably transfected mouse L cells by different constructs containing the human interferon β gene. When the construct was flanked by SAR elements, the gene transcription level was enhanced 20-30 fold with respect to the SAR-free construct, containing only the immediate regulatory elements.

However, the above-noted experiments have been limited to a very few examples of SAR elements, expressing mostly reporter genes, such as chloramphenicol acetyl transferase (CAT) or luciferase. SAR elements have not shown consistent results in their effect on the expression of target genes and some target gene sequences have been found to inhibit the effect of SAR elements (Klehr, et al., 1991, Biochemistry 30:1264).

SUMMARY OF THE INVENTION

The present inventor has significantly found that SAR elements may be used to increase the expression of recombinant mammalian EPO DNA. The present inventor constructed expression vectors carrying EPO genomic or cDNA sequences flanked by 3' and 5' human apolipoprotein B SAR elements. The expression vectors, when transfected into host cells resulted in increased expression of EPO compared to control host cells transfected with EPO expression vectors lacking SAR elements. Host cells transfected with expression vectors carrying an EPO cDNA sequence flanked by 3' and 5' SAR elements which expressed high levels of EPO were selected and cloned to obtain homogenous stable cell lines over-expressing EPO. Cloning produced stable cell lines expressing high levels of EPO, without the need for amplification. SAR elements have not, to the inventor's knowledge, heretofore been used for long term expression of a target gene in stable cell lines, or for the expression of recombinant EPO.

The present invention thus provides a recombinant DNA molecule adapted for transfection of a host cell comprising a nucleic acid molecule encoding mammalian erythropoietin, an expression control sequence operatively linked thereto and at least one SAR element. In an embodiment, the nucleic acid molecule encodes mammalian erythropoietin having the amino acid sequence shown in SEQ ID NOS 33 or 34 and FIG. 3B. In another embodiment, the nucleic acid molecule has the sequence as shown in SEQ ID NO. 33 or 35.

The SAR element is preferably a SAR element co-mapping with the chromatin domain boundary, such as the human apolipoprotein SAR elements, most preferably the SAR element comprises the sequence as shown in SEQ ID NO. 36 or 37 and FIGS. 5 or 6.

The present invention also provides an expression vector comprising a recombinant DNA molecule adapted for transfection of a host cell comprising a nucleic acid molecule encoding mammalian erythropoietin, an expression control sequence operatively linked thereto and at least one SAR element.

In an embodiment, the expression vector comprises a nucleic acid molecule encoding erythropoietin and having the sequence shown in SEQ ID NO. 35 and FIG. 4 under the control of the human cytomegalovirus IE enhancer and promoter and the beta-globin intron and, flanked by 5' and 3' apolipoprotein SAR elements.

In a further embodiment, the expression vector comprises a nucleic acid molecule encoding erythropoietin and having the sequence shown in SEQ ID NO. 35 and FIG. 4, flanked by 5' and 3' apolipoprotein SAR elements under the control of elongation factor--1 alpha promoter and intron.

The present invention still further provides a mammalian cell stably transfected with the expression vector of the invention. The mammalian cell may be any mammalian cell, for example CHO-K1, BHK, Namalwa. An aspect of the invention provides a mammalian cell, lacking multiple copies of an amplified selectable marker gene and capable of expressing recombinant EPO in vitro at levels of at least 1,500, preferably over 2,000, most preferably from 2,000 to 10,000 u/10⁶ cells in 24 hours.

In yet a further aspect, the invention provides a method of expressing recombinant mammalian erythropoietin comprising the steps of culturing a transfected mammalian cell of the invention in a suitable medium until sufficient amounts of erythropoietin are produced by the cell and separating the erythropoietin produced.

The present invention also relates to a method of preparing recombinant erythropoietin comprising transfecting a mammalian cell with an expression vector comprising a nucleic acid molecule encoding mammalian erythropoietin, an expression control sequence operatively linked thereto and at least one SAR element; culturing the transfected cell in a suitable medium until sufficient amounts of erythropoietin are produced by the cell and separating the erythropoietin produced. In a preferred embodiment, the erythropoietin is produced at levels of at least 2,000, most preferably form 2,000 to 10,000 u/10⁶ cells in 24 hours in the absence of gene amplification. The invention also relates to erythropoietin produced by the method of the invention.

In an embodiment of the method, the mammalian cell is further transfected with a selectable marker gene and transfected cells are selected in conditions where the activity of the product encoded by the selectable marker gene is necessary for survival of the cells. In a preferred embodiment, the selectable marker gene is pSV2neo.

In a further embodiment, the method comprises the additional step of identifying and selecting cells producing high levels of erythropoietin; cloning the selected cells; establishing long term cell lines from the selected cells and; culturing the selected cells in a suitable medium until sufficient amounts of erythropoietin are produced by the cell and separating the erythropoietin produced.

The present invention further provides a transgenic non-human animal or embryo whose germ cells and somatic cells contain a DNA construct comprising the recombinant DNA molecule of the invention.

DESCRIPTION OF THE DRAWINGS

The invention will be better understood with reference to the drawings in which:

FIG. 1A is a schematic representation of the procedure for synthesizing the erythropoietin gene;

FIGS. 1B-D show the DNA sequences of the oligonucleotides synthesized to construct the erythropoietin gene;

FIG. 2A is a schematic representation of the procedure for synthesizing the EPO_(short) sequence;

FIG. 2B is a schematic representation of the procedure for synthesizing the EPO_(Long) sequence;

FIG. 3A shows the DNA sequence of the erythropoietin gene; from 1-1860

FIG. 3B is a continuation of FIG. 3A showing the DNA sequence of the erythropoietin gene from 1861-3602;

FIG. 3C shows the amino acid sequence of the mature erythropoietin protein;

FIG. 4 shows the DNA sequence of the EPO_(long) sequence;

FIG. 5 shows the DNA sequence of the 3' SAR element of human apolipoprotein B;

FIG. 6 shows the DNA sequence of Rh10;

FIG. 7 shows a restriction map of the vector pLW18 and;

FIG. 8 shows a restriction map of the vector pLW19.

DETAILED DESCRIPTION OF THE INVENTION

As hereinbefore noted, the present inventor has significantly found that recombinant EPO expression is increased in host cells transfected with recombinant DNA encoding EPO operatively linked to an expression control sequence and SAR elements, compared to host cells transfected with EPO in the absence of SAR elements.

The present invention thus provides a recombinant DNA molecule adapted for transfection of a host cell comprising a nucleic acid molecule encoding mammalian erythropoietin, an expression control sequence operatively linked thereto and at least one SAR element. In a preferred embodiment the EPO is human EPO and in a particularly preferred embodiment the nucleic acid molecule has a sequence which encodes erythropoietin having the amino acid sequence as shown in SEQ ID NO 33 and 34 and FIG. 3C. In a particular embodiment, the nucleic acid molecule has the sequence as shown in SEQ ID NOS. 35 or 33.

1. Nucleic Acid Molecules Encoding Erythropoietin

The term "a nucleic acid molecule encoding mammalian EPO" as used herein means any nucleic acid molecule which encodes biologically active EPO. It will be appreciated that, within the context of the present invention, EPO may include various structural forms of the primary protein which retain biological activity. Biologically active EPO will include analogues of EPO having altered activity, for example having greater biological activity than EPO. Biological activity of EPO may be readily determined by the methods referred to herein.

Nucleic acid molecules encoding EPO include any sequence of nucleic acids which encode biologically active EPO, preferably, the nucleic acid molecule also encodes the leader sequence of the prepeptide to permit secretion of EPO from a cell transfected with the recombinant DNA molecule of the invention. The amino acid sequence of the leader sequence of the prepeptide is shown in SEQ ID NO. 33, from amino acid number -27 to -1. In an embodiment, the nucleic acid molecule encodes a peptide having the amino acid sequence as shown in SEQ ID NO. 33 and 34 and FIG. 3C. Nucleic acid molecules encoding EPO include the entire EPO gene sequence as shown in SEQ ID NO. 33, one or more fragments of this sequence encoding the EPO prepeptide (nucleotides 625-637, 1201-1346, 1605-1691, 2303-2482 and 2617-2772 in SEQ ID NO. 33) or the mature EPO peptide (nucleotides 1269-1346, 1605-1691,2303-2482 and 2617-2769 in SEQ ID NO. 33) or nucleic acid molecules having substantial homology thereto, or any fragment thereof encoding biologically active EPO, such as the EPO_(Long) sequence shown in SEQ ID NO. 35 and FIG. 4.

It will be appreciated that the invention includes nucleotide or amino acid sequences which have substantial sequence homology with the nucleotide and amino acid sequences shown in SEQ ID NOS: 33, 34 and 35 and FIGS. 3A, 3B, 3C and 4. The term "sequences having substantial sequence homology" means those nucleotide or amino acid sequences which have slight or inconsequential sequence variations from the sequences disclosed in SEQ ID NOS. 33, 34 and 35 i.e. the homologous sequences function in substantially the same manner to produce substantially the same polypeptides as the actual sequences. Due to code degeneracy, for example, there may be considerable variation in nucleotide sequences encoding the same amino acid sequence. The variations may be attributable to local mutations or structural modifications.

It will also be appreciated that a double stranded nucleotide sequence comprising a DNA segment of the invention or an oligonucleotide fragment thereof, hydrogen bonded to a complementary nucleotide base sequence, and an RNA made by transcription of this double stranded nucleotide sequence, are contemplated within the scope of the invention.

A number of unique restriction sequences for restriction enzymes are incorporated in the DNA sequence identified in SEQ ID NO: 33, and 35 and in FIGS. 3A and 3B, and 4 respectively, and these provide access to nucleotide sequences which code for polypeptides unique to EPO. DNA sequences unique to EPO or isoforms thereof, can also be constructed by chemical synthesis and enzymatic ligation reactions carried out by procedures known in the art.

Mutations may be introduced at particular loci for instance by synthesizing oligonucleotides containing a mutant sequence, flanked by restriction sites enabling ligation to fragments of the native sequence. Following ligation, the resulting reconstructed sequence encodes a derivative having the desired amino acid insertion, substitution, or deletion.

Alternatively, oligonucleotide-directed site-specific mutagenesis procedures may be employed to provide an altered gene having particular codons altered according to the substitution, deletion, or insertion required. Deletion or truncation derivatives of EPO may also be constructed by utilizing convenient restriction endonuclease sites adjacent to the desired deletion. Subsequent to restriction, overhangs may be filled in or removed, and the DNA religated. Exemplary methods of making the alterations set forth above are disclosed by Sambrook et al. (Molecular cloning A Laboratory Manual, 2d Ed., Cold Spring Harbor Laboratory Press, 1989).

The scope of the present invention also includes conjugates of EPO along with other molecules such as proteins or polypeptides. This may be accomplished, for example, by the synthesis of N-terminal or C-terminal fusion proteins or fragments of proteins to facilitate purification or identification of EPO (see U.S. Pat. No. 4,851,341, see also, Hopp et al., Bio/Technology 6:1204, 1988.) Thus, fusion proteins may be prepared by fusing through recombinant techniques the N-terminal or C-terminal of EPO or other portions thereof, and the sequence of a selected protein with a desired biological function. The resultant fusion proteins contain EPO or a portion thereof fused to the selected protein or portion thereof. Examples of proteins which may be selected to prepare fusion proteins include lymphokines such as gamma interferon, tumor necrosis factor, IL-1, IL-2,IL-3, IL-4, IL-5, IL-6, IL-7, IL-8, IL-9, IL-10, IL-11, GM-CSF, CSF-1 and G-CSF, nerve growth factor, protein A, protein G, GST and the Fc portion of immunoglobulin molecules.

Nucleic acid molecules encoding EPO may be chemically synthesized or may be cloned from a genomic or cDNA mammalian library using oligonucleotide probes derived from the known EPO sequences following standard procedures. In this manner, nucleic acid molecules encoding EPO may be obtained from the cells of a selected mammal.

For example, cDNA sequences encoding mammalian EPO may be isolated by constructing cDNA libraries derived from reverse transcription of mRNA in cells from the selected mammal which express EPO, for example adult kidney cells or foetal liver cells. Increased levels of expression in the cell may also be achieved, for example by inducing anemia in the mammal. DNA oligonucleotide probes may be used to screen the library for positive clones. Genomic DNA libraries may also be constructed and screened by plaque hybridization using fragments of EPO cDNA as probes.

Nucleic acid molecules which encode EPO may also be obtained from a variety of sources, including for example, depositories which contain plasmids encoding EPO sequences including the American Type Culture Collection (ATCC, Rockville Md.), and the British Biotechnology Limited (Cowley, Oxford England). EPO DNA as described in Lin, (1985, Proc. Natl. Acad. Sci. U.S.A. 82:7580) is deposited as HUMERPA, Accession No M11319.

Various post translational modifications are contemplated to the EPO encoded by the nucleic acid molecule. For example, EPO may be in the form of acidic or basic salts, or in neutral form. In addition, individual amino acid residues may be modified by, for example, oxidation or reduction. Furthermore, various substitutions, deletions, or additions may be made to the amino acid or DNA nucleic acid sequences, the net effect of which is to retain biological activity of EPO.

In a preferred embodiment of the invention, the nucleic acid molecule of the invention comprises the EPO_(Long) nucleotide molecule encoding EPO, shown in SEQ ID NO. 35 and FIG. 4. EPO_(Long) may be chemically synthesized by assembling short nucleotides, for example, as shown in FIG. 1B and SEQ ID NOS. 1 to 32. The procedure for the synthesis and assembly of the EPO_(Long) sequence from the short nucleotides is shown schematically in FIG. 2B.

2. SAR Elements

The term "SAR elements" as used herein refers to DNA sequences having an affinity or intrinsic binding ability for the nuclear scaffold or matrix. SAR elements are usually 300 or more base pairs long, require a redundancy of sequence information and contain multiple sites of protein-DNA interaction. Preferably SAR elements are found in non coding regions: in flanking regions or introns.

Suitable SAR elements for use in the invention are those SAR elements which promote elevated and position-independent gene activity in stable transfectants. SAR elements may be obtained, for example, from eukaryotes including mammals, plants, insects and yeast, preferably mammals. SAR elements are preferably selected which co-map with the boundaries of a chromatin domain. SAR elements co-mapping with the chromatin domain boundary are preferred for the recombinant DNA molecules of the invention to promote the formation of an independent domain containing the nucleic acid molecule encoding mammalian EPO to be expressed in stable transfectants.

Examples of preferred SAR elements which co-map with the chromatin domain boundary include the following: the 5' human apoB SAR element (Rh10), a Xbal fragment spanning nucleotides -5,262 to -2,735 of the human apoB gene, as shown in SEQ ID 37 and FIG. 6 and as described in Levy-Wilson and Fortier, 1989, (J. Biol. Chem. 264:21196). This region actually contains two SAR elements, a proximal and distal one. It is contemplated that either the proximal and distal SAR elements together or the distal element alone may be used. The 3' human apoB SAR element extends between nucleotides +43,186 and +43,850. The DNA sequence of this 665 bp region is described in Levy-Wilson and Fortier, 1989, supra and shown in SEQ ID NO. 36 and FIG. 5. A 60-bp deleted 3'human apoB SAR element (Rh32), is also suitable for use in the invention. The deletion is shown within brackets in FIG. 5.

Examples of suitable protocols for identifying SAR elements for use in the present invention are described below. The high salt method may be used to identify SAR elements by measuring the ability of labelled naked DNA fragments to bind nuclear matrices in the presence of unlabelled competitor DNA, typically E. coli DNA. DNA fragments bound to nuclear matrices under these conditions are operationally defined as SAR elements. The nuclear matrices may be isolated by the 2M NaCl extraction of DNAase I-digested nuclei (Cockerill and Garrard, 1986, Cell 44, 273-282). Chromosomal loop anchorage of the kappa immunoglobulin gene occurs next to the enhancer in a region containing topoisomerase II sites. (Cockerill, 1990, Nucleic. Acids. Res. 18, 2643-2648).

In the low salt method for identifying SAR elements nuclei are heated to 37° C. and then extracted with a buffer containing 25 mM 3,5-diiodosalicylic acid lithium salt (LIS) which removes histones. The LIS-treated nuclei are extracted several times with a low salt buffer. The extracted nuclei are digested with restriction endonucleases. The solubilized (non-matrix bound) DNA fragments are removed by centrifugation. Southern blot hybridization with labelled probes identifies the DNA fragments bound to the nuclear matrix (Mirkovitch et al., 1984, Cell 39, 223-232). Both the above-noted methods yield essentially the same result, that is, a sequence identified as a SAR element with the high salt method will also be identified as a SAR element by the Lis-low salt method.

The SAR element may be inserted into the recombinant molecule of the invention upstream or downstream from the nucleic acid molecule encoding EPO and the operatively linked expression control sequence. Preferably, the SAR element is inserted within 0.1 to 100 kb upstream or downstream, more preferably from 0.1 to 50 kb, most preferably 0.5 to 10. In a preferred embodiment, more than one SAR element should be inserted into the recombinant molecule of the invention, preferably the SAR elements should be located in flanking positions both upstream and downstream from the nucleic acid molecule encoding EPO and the operatively linked expression control sequence. The use of flanking SAR elements in the nucleic acid molecules may allow the SAR elements to form an independent loop or chromatin domain, which is insulated from the effects of neighbouring chromatin. Accordingly, EPO gene expression may be position-independent and the level of expression should be directly proportional to the number of integrated copies of the recombinant DNA molecules of the invention. Preferably, the SAR elements should be inserted in non-coding regions of the recombinant DNA molecule.

The recombinant DNA molecules of the invention may be advantageously used to express elevated levels of mammalian EPO. Routine procedures may be employed to confirm that the SAR elements selected by the above-noted protocols are useful for expressing elevated levels of mammalian EPO. For example, appropriate expression vectors comprising a nucleic acid molecule encoding mammalian erythropoietin and an expression control sequence operatively linked thereto may be constructed with and without (control vectors) SAR elements. Mammalian host cells may be stably transfected with an EPO expression vector having a selectable marker gene or may be stably co-transfected with an EPO expression vector and a selectable marker gene vector, such as a pSV2-neo vector (which carries the gene conferring the resistance to the antibiotic G-418). The levels of EPO secreted may be determined, for example, by RIA and the effect of the flanking SAR elements on EPO production may be determined. Transfected cell populations producing the highest levels of EPO as detected by RIA, may be selected and subjected to successive rounds of cloning by the dilution method.

3. Expression Control Sequences

Suitable expression control sequences may be derived from a variety of mammalian sources. Selection of appropriate regulatory elements is dependent on the host cell chosen, and may be readily accomplished by one of ordinary skill in the art. Examples of regulatory elements include: a transcriptional promoter and enhancer or RNA polymerase binding sequence, splice signals, polyadenylation signals, including a translation initiation signal. Additionally, depending on the host cell chosen and the vector employed, other genetic elements, such as an origin of replication, additional DNA restriction sites, enhancers, sequences conferring inducibility of transcription, and selectable markers, may be incorporated into the expression vector.

Strong promoters (or enhancer/promoters) are preferably selected. A strong promoter is one which will direct the transcription of a gene whose product is abundant in the cell. The relative strength and specificities of a promoter/enhancer may be compared in comparative transient transfection assays. In an embodiment, a promoter may be selected which has little cell-type or species preference and which can therefore be strong when transfected into a variety of cell types.

In preferred embodiments of the invention, the EF1 promoter or the human cytomegalovirus. (HCMV) IE (immediate-early) enhancer and promoter may be used. The human EF-1α gene promoter is stronger than the adenovirus major late promoter in a cell free system (Uetsuki et al., 1989, J. Biol. Chem. 264:5791). The EF1 promoter is the promoter for the human chromosomal gene for the polypeptide chain elongation factor-1α: extending from -303 to -1 for genomic constructs and from -303 to +986 for cDNA constructs. For the cDNA constructs, the EF1 DNA sequence includes the promoter as well as exon 1 and intron 1 (Uetsuki et al, 1989, J. Biol. Chem. 264, 5791-5798). The human cytomegalovirus (hCMV) IE (immediate-early) enhancer and promoter, extend from -598 to +54 in the sequence (Kay and Humphries, 1991, Methods in Molecular and Cellular Biology 2, 254-265).

4. Methods of Expressing EPO

As hereinbefore noted, the present invention also provides expression vectors which include the recombinant DNA molecule of the invention and mammalian cells stably transfected with the expression vector.

Suitable expression vectors, such as plasmids, bacteriophage, retroviruses and cosmids are known in the art. Many plasmids suitable for transfecting host cells are well known in the art, including among others, pBR322 (see Bolivar et al., Gene 2:9S, 1977), the pUC plasmids pUC18, pUC19, pUC118, pUC119 (see Messing, Meth in Enzymology 101:20-77, 1983 and Vieira and Messing, Gene 19:259-268, 1982), and pNH8A, pNH16a, pNH18a, and Bluescript M13 (Stratagene, La Jolla, Calif.). Retroviral vectors are reviewed in Eglitis and Anderson, 1988, Biotechniques 6:608. Suitable expression vectors are those which are stably incorporated into the chromosome of the mammalian host cell.

The recombinant DNA molecule of the invention may be expressed by a wide variety of mammalian cells. Methods for transfecting such cells to express foreign DNA are well known in the art (see, e.g., Itakura et al., U.S. Pat. No. 4,704,362; Hinnen et al., PNAS USA 75:1929-1933, 1978; Murray et al., U.S. Pat. No. 4,801,542;

Upshall et al., U.S. Pat. No. 4,935,349; Hagen et al., U.S. Pat. No. 4,784,950; Axel et al., U.S. Pat. No. 4,399,216; Goeddel et al., U.S. Pat. No. 4,766,075; and Sambrook et al. Molecular Cloning A Laboratory Manual, 2nd edition, Cold Spring Harbor Laboratory Press, 1989, all of which are incorporated herein by reference). Suitable expression vectors include vectors having a selectable marker gene.

Mammalian cells suitable for carrying out the present invention include, among others: COS (e.g., ATCC No. CRL 1650 or 1651), BHK (e.g., ATCC No. CRL 6281), CHO-K1 (ATCC No. CCL 61), HeLa (e.g., ATCC No. CCL 2), 293 (ATCC No. 1573) and NS-1 cells. As noted above, suitable expression vectors for directing expression in mammalian cells generally include a promoter, as well as other transcriptional and translational control sequences. Common promoters include SV40, MMTV, metallothionein-1, adenovirus Ela, CMV, immediate early, immunoglobulin heavy chain promoter and enhancer, human cytomegalovirus 1E enhancer and promoter and RSV-LTR. Protocols for the transfection of mammalian cells are well known to those of ordinary skill in the art. Representative methods include calcium phosphate mediated gene transfer, electroporation, retroviral, and protoplast fusion-mediated transfection (see Sambrook et al., supra).

Given the teachings provided herein, promoters, terminators, and methods for introducing expression vectors of an appropriate type into mammalian calls may be readily accomplished. Accordingly, the invention also relates to mammalian cells stably transfected with an expression vector of the invention. The term "stably transfected" refers to the fact that suitable expression vectors are those which stably incorporate the recombinant DNA molecule of the invention into the chromosomes of the mammalian cell.

The invention also relates to a mammalian cell lacking a selectable marker gene capable of being amplified and, capable of expressing recombinant EPO in vitro at levels of at least 1,500, preferably at least 2,000, most preferably 2,000 to 10,000 u/10⁶ cells in 24 hours.

In an embodiment, the invention also relates to a mammalian cell, having less than 1,000, preferably less than 100, most preferably less than 10 copies of a selectable marker gene and capable of expressing recombinant EPO in vitro at levels of at least 1,500, preferably at least 2,000, most preferably 2,000 to 10,000 u/10⁶ cells in 24 hours.

Amplification refers, for example, to the process of culturing cells in appropriate medium conditions to select cells resistant to the drug methotrexate. Such cells have been found to be resistant to methotrexate due to an amplification of the number of their gene encoding dihydrofolate reductase (DHFR). Selection for cells resistant to methotrexate produces cells containing greater numbers of DHFR genes. Passenger genes, such as the EPO gene carried on the expression vector along with the DHFR gene or co-transfected with the DHFR gene may also be increased in their gene copy number. Cells which have been amplified thus have multiple copies of the selectable marker gene in addition to the passenger gene.

It is an advantage of the present invention that high levels of EPO expression may be achieved without the need for amplification. Thus the mammalian cells of the invention express high levels of EPO and do not express high levels of a selectable marker gene. The expression of high levels of selectable marker genes in amplified cells may interfere with the cell's ability to remain stable in long term culture and to express high levels of EPO in long term culture. Amplified cells may carry certain disadvantages such as non-specific toxicity associated with exposure of the cells to the inhibitory drug or compound.

Selectable marker genes which may be amplified in a mammalian host cell are known in the art and include the genes encoding proteins conferring resistance to chloramphenicol (Wood et al., CSHSQB 51:1027, 1986), methotrexate (Miller, MC Biol., 5:431, 1985; Corey et al., Blood 75:337, 1990; Williams et al., Proc. Natl. Acad. Sci. USA, 83:2566, 1986; Stead et al., Blood 71:742, 1988), mycophenolic acid (Stuhlmann et al., Proc. Natl. Acad. Sci. USA 81:7151, 1984), or various chemotherapeutic agents (Guild et al., Proc. Natl. Acad. Sci USA 85:1595, 1988; Kane et al., Gene 84:439, 1989; Choi et al., Proc. Natl. Acad. Sci. USA; Sorrentino, et al., Science 257:99, 1992). A discussion of selectable marker genes, including those capable of being amplified is provided in Kreigler, 1990, "Gene Transfer and Expression, A Laboratory Manual", Chapter 6, Stockton Press, and include the gene encoding dihydrofolate reductase.

Within another aspect, the present invention relates to a method of preparing recombinant erythropoietin comprising transfecting a mammalian cell with an expression vector comprising a nucleic acid molecule encoding mammalian erythropoietin, an expression control sequence operatively linked thereto and at least one SAR element; culturing the transfected cell in a suitable medium until sufficient amounts of erythropoietin are produced by the cell and separating the erythropoietin produced. In an embodiment, the mammalian cell may be further transfected with a selectable marker gene and the transfected cells may be selected by means of the selectable marker gene. Examples of selectable marker genes are given above and include neo.

In an embodiment of the method, cells producing high levels of erythropoietin may be identified and selected and subcloned to establish long term cell lines from the selected cells and; the selected cells may be cultured in a suitable medium until sufficient amounts of erythropoietin are produced by the cell. EPO produced may then be separated from the medium.

It is an advantage of the method of the invention that cell lines may be established which are stable over the long term, at least six months. The long term cell lines of the invention express consistently high levels of EPO and may be maintained without the selective pressure often required to maintain the high copy number of amplified genes in cell lines which have been subjected to amplification.

EPO may be prepared by culturing the host/vector systems described above, in order to express the EPO. Recombinantly produced EPO may be further separated and further purified as described in more detail below.

Biologically active EPO expressed may be assayed by known procedures such as tritiated thymidine uptake by mouse spleen cell erythrocyte precursors (Krystal, et al., 1986, Blood 67:71); the exhypoxic mouse method using ⁵⁹ Fe incorporation into erythrocyte precursors (Cotes and Bangham, 1961, Nature 191:1065); ⁵⁹ Fe uptake into fetal mouse liver cells (Dunn et al, 1975, Exp. Hematol. 3:65); and the starved rat method (Goldwasser and Gross, 1975, Methods Enzymol. 37:109). EPO once expressed may also be quantitated, for example by RIA, separated and purified by known techniques such as ultrafiltration, flat-bed electrofocusing, gel filtration, electrophoresis, isotachophoresis and various forms of chromatography, such as ion exchange, adsorption chromatography, column electrophoresis and various forms of HPLC. Procedures for the chromatographic separation of EPO are described, for example in U.S. Pat. No 4,667,016.

The present invention also relates to transgenic non-human mammals or embryos whose germ cells and somatic cells contain a DNA construct comprising the recombinant DNA molecule of the invention. The recombinant DNA molecule of the invention may be expressed in non-human transgenic animals such as mice, rats, rabbits, sheep, cows and pigs (see Hammer et al. (Nature 315:680-683, 1985), Palmiter et al. (Science 222:809-814, 1983), Brinster et al. (Proc Natl. Acad. Sci USA 82:44384442, 1985), Palmiter and Brinster (Cell. 41:343-345, 1985) and U.S. Pat. No. 4,736,866). Briefly, an expression unit, including a DNA sequence to be expressed together with appropriately positioned expression control sequences, is introduced into pronuclei of fertilized eggs. Introduction of DNA is commonly done by microinjection. Integration of the injected DNA is detected by blot analysis of DNA from tissue samples, typically samples of tail tissue. It is preferred that the introduced DNA be incorporated into the germ line of the animal so that it is passed on to the animal's progeny. Tissue-specific expression may be achieved through the use of a tissue-specific promoter, or through the use of an inducible promoter, such as the metallothionein gene promoter (Palmiter et al., 1983, ibid), which allows regulated expression of the transgene. Alternatively, yeast artificial chromosomes (YACs) may be utilized to introduce DNA into embryo-derived stem cells by fusion with yeast spheroblasts carrying the YAC (see Capecchi, Nature 362:255-258, 1993; Jakobovits et al., Nature 362:255-258, 1993). Utilizing such methods, animals may be developed which express EPO in tissues. Tissue specific promoters may be used to target expression of EPO in cells. Tissue specific promoters include the 5' or 3' flanking sequences of the beta-globin, elastase, alpha-fetoprotein, alpha-A crystalline, an erythroid specific transcriptional element and insulin genes (Yee, et al. (1989) P.N.A.S., U.S.A. 86, 5873-5877; Swift, et al. 1984, Cell 38:639; Storb et al., Nature (Lond.) 310:238; Grosscheldl et al., 1985 Cell 41:885; Shani, 1985 Nature (Lond) 314:238 and Chada et al, 1985, Nature (Lond)). The use of SAR elements in the development of transgenic animals is described for example in Xu, 1989, J. Biol. Chem. 264:21190; McKnight et al., 1992, Proc. Natl. Acad. Sci. U.S.A. 89:6943; Brooks, et al., 1994, Mol. Cell. Biol. 14:2243 and; Forrester, et al., 1994, Science 265:1221.

In a preferred embodiment suitable promoters and/or enhancers may be selected from mammary gland specific genes which are normally only expressed in milk, for example the genes encoding α-casein (Gene Pharming, Leiden, Netherlands), β-casein (Genzyme Transgenics Corp. Framingham, Mass.), γcasein, κ-casein α-lactablbumin β-lactalbumin β-lactogloblin (PPL Therapeutics Ltd, Edinburgh, Scotland) and whey acidic protein (Altra Bio Inc., Arden Hills Minn.). Methods for targeting recombinant gene expression to the mammary gland of a mammal are described, for example, in U.S. Pat. No. 5,304,489. Briefly, a DNA construct with the recombinant DNA molecule of the invention comprising a mammary gland specific promoter may be microinjected into a newly fertilized egg leading to integration of the construct into the genome and secretion of the protein into the milk of a mature lactating female. EPO expressed in the milk may be purified from the milk using standard procedures after skimming off the milk fat, separating out the caseins and precipitating EPO out of the whey fraction, followed by standard protein purification procedures for EPO as described elsewhere herein.

A major problem in the generation of transgenic mammals for the expression of recombinant proteins has been the varying levels of expression which result due to chromosomal factors in the local environment where the construct integrates, for example regulatory elements and the state of the chromatin (open or closed). As a result, generating a transgenic mammal that produces high levels of a recombinant protein has been achieved only by laborious trial and error.

The present invention provides a transgenic non-human animal whose germ cells and somatic cells contain a DNA construct comprising the recombinant DNA molecules of the invention, comprising a tissue specific promoter, preferably the tissue specific promoter is a promoter which specifically expresses EPO in milk. In a particularly preferred embodiment, the recombinant molecule contained in the transgenic non-human mammal comprises the nucleic acid molecule encoding EPO and the expression control sequence operatively linked thereto, flanked by SAR elements. An advantage of DNA constructs having flanking SAR elements is that expression of EPO may be independent of the site of integration of the construct as the construct is insulated from surrounding chromosome material by the SAR elements, which define an open chromatin domain.

5. Applications

It will be apparent that the recombinant DNA molecules, expression vectors, transfected host cells, methods and transgenic animals of the invention will be useful for the efficient expression and production of recombinant mammalian EPO in vitro and in vivo as described above.

Recombinant EPO may be used to treat animals and human patients, including patients having anemia as a result of chronic renal failure. As EPO is the primary regulator of red blood cell formation, it has applications in both the diagnosis and treatment of disorders of red blood cell production and has potential applications for treating a range of conditions such as anemia, sickle cell disease, conditions where red cells are depleted (for example in bone marrow transplants), thalassemia, cystic fibrosis, menstrual disorders, acute blood loss and conditions involving abnormal erythropoiesis (for example cancers of the haemopoietic system), conditions involving destruction of red blood cells by over exposure to radiation, reduction in oxygen intake at high altitudes, complications or disorders secondary to AIDS and prolonged unconsciousness.

The recombinant DNA molecules, expression vectors and transformed mammalian cells of the invention will also have useful applications in gene therapy, whereby a functional EPO gene is introduced into a mammal in need thereof, for example mammals having anemias. The transfer of the recombinant DNA molecule of the invention into mammalian cells may be used, for example in gene therapy to correct an inherited or acquired disorder through the synthesis of missing or defective EPO gene products in vivo.

The recombinant DNA molecule of the invention may be used in gene therapy as briefly described below. The recombinant DNA molecule may be introduced into cells of a mammal, for example haemopoietic stem cells removed from the bone marrow or blood of the mammal. Hemopoietic stem cells are particularly suited to somatic gene therapy as regenerative bone marrow cells may be readily isolated, modified by gene transfer and transplanted into an immunocompromised host to reconstitute the host's hemopoietic system. Suitable hemopoietic stem cells include primitive hemopoietic stem cells capable of initiating long term culture (Sutherland et al., Blood, Vol. 74, p. 1563, 1986 and Udomsakdi et al., Exp. Hematol., Vol. 19, p. 338, 1991.) Suitable cells also include fibroblasts and hepatocytes.

The recombinant DNA molecules of the invention may be introduced into the cells by known methods, including calcium phosphate mediated transfection described herein or retroviral mediated uptake. The recombinant DNA molecule of the invention may be directly introduced into cells or tissues in vivo using delivery vehicles such as retroviral vectors, adenoviral vectors and DNA virus vectors. They may also be introduced into cells in vivo using physical techniques such as microinjection and electroporation or chemical methods such as coprecipitation and incorporation of DNA into liposomes. Recombinant molecules may also be delivered in the form of an aerosol or by lavage. The recombinant DNA molecules of the invention may also be applied extracellularly such as by direct injection into cells. Freed et al., New Eng. J. Med. 327(22):1549-1555, 1992, describe a method for injecting fetal cells into brains of Parkinson's patients. Gene therapy involving bone marrow transplant with recombinant primary hemopoietic stem cells requires efficient gene transfer into the stem cells. As a very small number of primary stem cells can reconstitute the entire host hemopoietic system it is important that the transferred gene be efficiently expressed in the recombinant stem cells transferred. Thus it is expected that the recombinant molecules of the invention will be particularly advantageous for use in gene therapy to correct defects in the erythropoietin gene.

As hereinbefore noted, the recombinant DNA molecules of the invention, having flanking SAR elements, are particularly useful for the expression of EPO in transgenic mammals and therefore they are particularly useful in gene therapy as the SAR elements define an open chromatin domain and insulate the construct from the surrounding chromosome material, thereby, providing position-independent expression.

The following non-limiting examples are illustrative of the present invention:

EXAMPLES Example 1 Synthesis of EPO cDNA Sequences

EPO Oligonucleotide synthesis

EPO oligonucleotides were synthesized with the Applied Biosystems Inc. 392 DNA/RNA Synthesizer at the 0.2 μm scale (.sup.˜ 500 μg). Oligonucleotide 5' ends were phosphorylated, except for the ones coinciding with the 5' ends of each of the four blocks. Oligonucleotides lacking 5' phosphorylation were purified using the Applied Biosystems Oligo Purification Cartridge (OPC). Oligonucleotides with 5' phosphorylation were purified from acrylamide gels (according to the protocol described in Sambrook, Fritsch, and Maniatis, 1989. Molecular Cloning: A Laboratory Manual, 2nd Edition. Cold Spring Harbor Laboratory Press, pp. 11.23 -11.30). C₁₈ Sep-Pak cartridges from Millipore were used to remove salts. All oligos were resuspended in double distilled H₂ O.

Oligonucleotides EPO1 (SEQ ID NO. 1), EPO2 (SEQ ID NO. 2), EPO3 (SEQ ID NO. 3), EPO4 (SEQ ID NO. 4), EPO5 (SEQ ID NO. 5), EPO6 (SEQ ID NO. 6), EPO7 (SEQ ID NO. 7), EPO8 (SEQ ID NO. 8), EPO9 (SEQ ID NO. 9), EPO10 (SEQ ID NO. 10), EPO11 (SEQ ID NO. 11), EPO12 (SEQ ID NO. 12), EPO13 (SEQ ID NO. 13), EPO13b (SEQ ID NO. 14), EPO14 (SEQ ID NO. 15), EPO15 (SEQ ID NO. 16), EPO1α (SEQ ID NO. 17), EPO2α (SEQ ID NO. 18), EPO3α (SEQ ID NO. 19), EPO4α (SEQ ID NO. 20), EPO5α (SEQ ID NO. 21), EPO6α (SEQ ID NO. 22), EPO7α (SEQ ID NO. 23), EPO8α (SEQ ID NO. 24), EPO9α (SEQ ID NO. 25), EPO10α (SEQ ID NO. 26), EPO11α (SEQ ID NO. 27), EPO12α (SEQ ID NO. 28), EPO13α (SEQ ID NO. 29), EPO13Bα (SEQ ID NO. 30 EPO14α (SEQ ID NO. 31) and EPO15α (SEQ ID NO. 32) as shown in FIGS. 1B, 1C and 1D were synthesized. All oligonucleotides labelled with "α" are for the complementary strand (i.e. negative sense of the EPO gene). Oligonucleotides EPO1 (SEQ ID NO. 1), EPO1α (SEQ ID NO. 17), EPO15 (SEQ ID NO. 16) and EPO15α (SEQ ID NO. 32) contain extra bases at their 5'-ends and 3'ends, respectively, which facilitate construction of a HindIII recognition site.

Assembly of blocks 1, 2, 3 and 4

Blocks 1, 2, 3, and 4 as shown in FIG. 1A were synthesized by ligating the above-noted EPO oligonucleotides according to the following protocol.

40 pmoles of each oligonucleotide were mixed in a microcentrifuge tube in a final volume of 50 μl. The oligonucleotides were annealed by heating at 98° C. for 5 minutes in a heat block. The heat block containing the tube was removed from the heating unit and allowed to cool on the benchtop to 30° C. (approximately 1.5 hrs). 6 μl of 10×T₄ DNA ligase buffer (0.5M Tris-HCl, pH 7.8, 0.1M MgCl₂, 0.1M DTT, 10 mM ATP and 250 μg/ml BSA), was added to 2 μl (or 2 units) of T₄ DNA ligase, and brought to volume to 60 μl with double distilled H₂ O and incubated overnight at 14° C. The mixture was heated at 75° C. for 10 minutes to inactive ligase and then cooled on ice to dissociate non ligated oligonucleotides and ethanol precipitate.

Blocks 1, 2, 3 and 4 were purified as follows. Each ligation mix was run on a 3% low melting agarose gel. No band of the expected size was visible on the gel. However, DNA was extracted from the region of the gel where the gene block was expected to be. The rationale was that there was a small amount of the correct gene block present.

The DNA extracted from the agarose gel was amplified by the polymerase chain reaction (with the NE Biolabs Vent DNA polymerase, 1 cycle 30 sec at 98° C., 25-30 cycles 30 sec at 98° C., 40 sec at 50°.sup.˜55 ° C. and 2 min at 72° C., 1 cycle 10 min at 72° C., and cooled at 6° C. The primers were complementary to the ends of the gene blocks and contained a few extra bases so that the entire recognition sites for the specific restriction enzymes flanking each block would be present in each complete block. Blocks were then cloned into the SmaI site of pUC18 or pUC19 plasmids.

Assembled gene blocks were sequenced by the dideoxy-terminator method (Sanger, and Coulson, 1975, J. Mol. Biol. 94, 441-448). Typically, 5-12 clones had to be sequenced for each gene block in order to identify one with the expected sequence.

EPO cDNA sequences were assembled as described in Example 2 herein. EPO_(short) and EPO_(Long) cDNA were assembled into pUC18 as shown in FIGS. 2A and 2B, to generate pLW20 and pLW21, respectively.

Example 2 Assembly of Expression Vectors

Synthesis and assembly of EPO cDNA

Two EPO cDNA sequences were chemically synthesized: EPO_(short) and EPO_(Long). The reason for making both a long and a short version of the gene was based on previous results while expressing another gene in COS cells. It had been noted that reducing the length of the 3' non-coding sequence coincided with increased expression of the gene. However, this was not observed with EPO. Therefore the constructs used for this example contained the EPO_(Long) cDNA, as shown in SEQ ID NO. 35 and FIG. 4.

FIG. 1A, provides a schematic representation of the synthesis and assembly of the EPO_(Long) cDNA sequence (SEQ ID NO. 35 and FIG. 4) from the oligonucleotides. Briefly, the coding and complementary strands from contiguous oligonucleotides which had an average length of 60 bases were synthesized. The breakpoints between the oligonucleotides were chosen such that when two complementary oligonucleotides annealed, cohesive ends compatible with those of the adjoining oligonucleotide pair were created. The EPO_(Long) cDNA (SEQ ID NO. 35 and FIG. 4) was constructed from fifteen oligonucleotide pairs, shown in FIG. 1B and SEQ ID NOS. 1-32). The coding strand oligonucleotides were numbered from 1 to 15 except for 13 which was replaced with 13b, and the complementary strand oligonucleotides were numbered 1α to 15α except for 13α which was replaced with 13bα.

The fifteen oligonucleotide pairs were assembled in four blocks. Each junction between adjacent blocks constitutes a unique restriction site. Only three silent mutations were introduced into the EPO_(Long) cDNA sequence for the creation of unique restriction sites: (1) C at position 22 was replaced with A, to add a BstXI site, (2) C at position 256 was replaced with T, to remove a PstI site, and (3) C at position 705 was replaced with T, to add a SspI site. The assembly of the four blocks was done in PUC18, leading to the vector pLW21. pLW21 is the pUC18 vector with the 788 bp EPO_(Long) cDNA sequence, as shown in SEQ ID NO. 35 and FIG. 4, inserted in the HindIII restriction site.

Isolation of genomic EPO DNA

A human leukocyte genomic library was purchased from Clontech and was screened by plaque hybridization with fragments of EPO cDNA as probes. A 2.4 kb (2,365 bp) EPO genomic clone was isolated. This clone spans the HUMERPA sequence (Genbank, accession number M11319) (SEQ ID NO. 33 and FIGS. 3A and 3B) from nucleotide 499 to nucleotide 2365, that is to say its 5' end maps 126 nucleotides upstream of the ATG initiation coding of the EPO pre-protein. The rationale for isolating the EPO gene was that the length of the DNA between the SAR elements would be longer and might allow for an increased effect of the SAR elements.

SAR elements

Two human apolipoprotein B (apoB) SAR elements were used which co-map with the boundaries of the human apolipoprotein B gene chromatin domain (Levy-Wilson & Fortier, 1989, J. Biol. Chem. 264:21196). The following clones were used: Rh10 carrying the distal 1212 bp-long 5'human apoB SAR element and 1317 bp of proximal sequence (SEQ ID NO. 37 and FIG. 6) and a clone (Rh32) carrying the 605 bp long 3'hu apoB SAR element (SEQ ID NO. 36 and FIG. 5).

The DNA sequence of Rh10 was determined by dideoxy-terminator method (Sanger, F. and Coulson, A. R., 1975, J. Mol. Biol. 94:441) and is shown in SEQ ID NO. 37 and FIG. 6. The 2529 bp Rh10 sequence consists of the 1212 bp 5' distal human apoB SAR elements and the 1317 bp 5' proximal sequence in the 5' to 3' orientation. The DNA sequence of Rh32 was also determined, and was found to be identical to the sequence published in Levy-Wilson & Fortier (1989, J. Biol. Chem. 264:21196) (SEQ ID NO. 36 and FIG. 5), except for a 60 base pair deletion spanning nucleotides 259 to 318, shown within brackets in FIG. 5. Contrary to Rh10 which is not a typical SAR sequence, Rh32 is A/T rich and contains 22 copies of the ATATTT motif.

Regulatory Elements of Expression Vectors

Two basic expression vectors were derived from epAX111 and pAX142 (renamed pLW19 or pSB3 and pLW18 or pSB2, respectively). pAX111 (Kay & Humphries, Methods Mol. Cell. Biol. 2:254, 1991) carries the human cytomegalovirus IE enhancer and promoter and the β-globin intron, while pAX142 carries the elongation factor-1α promoter and intron. For each of these vectors there are single restriction sites located on each site of the EPO transcription unit, where the SAR elements were introduced (SpeI or EcoRV at the 5'end and HpaI at the 3'end). Maps of the two vectors pLW18 (pSB2) and pLW19 (psB3) are shown in FIGS. 7 and 8 respectively.

Assembly of Expression Vectors

The EPO_(Long) cDNA sequence (SEQ ID NO.35, FIG. 4) or the genomic EPO DNA (SEQ ID NO. 33, FIGS. 3A and 3B) were introduced clockwise into the cloning sites of the expression vectors. In the case of the genomic clones, the β-globin and EF1 introns were removed from the pSB3 and pSB2 vectors, respectively. A summary of the expression vectors is shown in Table 1.

Construction of pLW24 and pLW25 Vectors

The EPO_(Long) cDNA (SEQ ID NO.35, FIG. 4) was removed from pLW21 by digestion with HindIII, was blunt-ended with the T4 DNA polymerase and was introduced in the clockwise orientation into the SmaI site of pLW18 and pLW19 to generate pLW24 and pLW25, respectively.

Construction of p24MAR1 and p25MAR1

Introduction of the 5' human apoB SAR element at the 5' end of the EPO transcription unit was accomplished as follows. The 2,529 bp XbaI fragment from Rh10 (SEQ ID NO. 37, FIG. 6) was introduced in the clockwise orientation into the SpeI site of pLW24 and pLW25 to generate p5MAR24 and p5MAR25, respectively (Note that XbaI and SpeI sites are compatible).

Introduction of the 60 bp-deleted 3' human apoB SAR element at the 3' end of the EPO transcription unit was accomplished as follows. The 605 bp DraI-RsaI fragment from the plasmid 12 DI Eco was added XhoI linkers and cloned into the XhoI site of the Stratagene pSBII SK(+) plasmid, to generate plasmid 3'apoBX (Rh32) (SEQ ID NO. 36, FIG. 5). The .sup.˜ 605 bp SAR fragment was then removed from Rh32 by XhoI digestion, blunt-ended with the Klenow enzyme and cloned into the HpaI site of p5MAR24 and p5MAR25 to generate p24MAR-1 and p25MAR-1, respectively. The orientation of the inserted fragments has not yet been determined.

Construction of pAP142 and DAP140

Plasmids pSB2 and pSB3 were derived from pLW18 and pLW19, respectively. A 12 bp DNA linker with the EcoRV and SphI restriction sites was inserted into the KpnI site of pLW18 and pLW19 to generate pSB2 and pSB3, respectively. This allowed for introduction of SAR elements into the blunt-end EcoRV restriction site, just upstream of the EPO transcription unit.

The EPO_(Long) cDNA sequence was removed from pLW24 by digestion with Sall and cloned in the clockwise orientation into the Sall site of pSB2 to generate pAP13. pAP5 was generated by removing the EPO_(Long) cDNA sequence from pLW25 by digestion with BamHI and cloning in the clockwise orientation into the BamHI site of pSB3 to generate pAP5.

The Rh32 .sup.˜605 bp XhoI SAR fragment (60 bp-deleted 3' human apoB SAR element) was blunt-ended with the T4 DNA polymerase and inserted in the clockwise orientation into the EcoRV site of PAP13 and pAP5 to generate pAP138 and pAP136, respectively. The same Rh32 .sup.˜605 bp XhoI blunt-ended SAR fragment was inserted in the clockwise orientation into the HpaI site of pAP138 and pAP136 to generate pAP142 and pAP140, respectively.

Construction of pAP59 and pAP67

pAP42 is an intronless version of pSB2. pSB2 was amplified by the polymerase chain reaction between nucleotides 1308 and 321, and the amplified fragment was ligated on itself to produce pAP42. pAP43 is an intronless version of pSB3. The SmaI-XmnI fragment (nucleotides 677 -1320) was removed from pSB3 to produce pAP43.

The EPO genomic clone was isolated from a Clontech library (Cat. No. HL1006d; Lot No. 19412) by probing with the BamHI EPO_(short) cDNA fragment from pAP4. The EPO_(short) cDNA fragment used as a probe to isolate the genomic EPO clone was a BamHI fragment from pAP4. As for EPO_(Long) cDNA, EPO_(short) cDNA was first assembled into the HindIII site of the pUC18 vector, to generate the pLW20 vector, blunt-ended with the T4 DNA polymerase and inserted in the clockwise orientation into the SmaI site of pLW19 to generate pLW23. Then the EPO_(short) cDNA sequence was removed from pLW23 by BamHI digestion and cloned in the clockwise orientation into the BamHI site of pSB3 to generate pAP4.

Plaque hybridization was performed according to the method described in "Molecular Cloning. A Laboratory Manual, 2nd Edition. 1989". Edited by Sambrook, Fritsch, and Maniatis, Cold Spring Harbor Laboratory Press. pp 2.108-2.121. A 7.5 kb BamHI fragment (cloned in the Stratagene pBS (KS+) plasmid) was identified as an EPO genomic clone. The identity of this clone was confirmed by polymerase chain reaction between primers EPOGEN 1 (nucleotides 499-518 in HUMERPA sequence) and EPOGEN 12 (nucleotides 2848-2863, on complementary strand, in HUMERPA sequence). This resulted in the expected fragment. The 2,365 bp amplified fragment was cloned in the clockwise orientation into the HincII site of pUC19 to generate pAP41. The EPO genomic sequence was then removed from pAP41 by EcoRI and HindIII digestion, blunt-ended with the T4 DNA polymerase and inserted in the clockwise orientation into the SmaI site of pAP42 to generate pAP59 or into the blunt-ended BamHI site of pAP43 to generate pAP67.

Construction of pAP123, pAP127, pAP132 and pAP134

The Rh32 .sup.˜605 bp XhoI SAR fragment (60 bp-deleted 3' human apoB SAR element) was blunt-ended with the T4 DNA polymerase and inserted in the clockwise orientation into the HpaI site of pAP59 and pAP67 to generate pAP117 and pAP119, respectively. The same Rh32 .sup.˜ 605 bp XhoI blunt-ended SAR fragment was inserted in the clockwise orientation into the EcoRV site of pAP117 and pAP119 to generate pAP123 and pAP127, respectively.

The 2,529 bp XbaI fragment from Rh10 was blunt-ended with the T4 DNA polymerase, and introduced in the clockwise orientation into the EcoRV site of pAP117 and pAP119 to generate pAP132 and pAP134, respectively.

Example 3 Transfection and Expression of EPO

Transfection

Briefly as described in more detail below CHO-K1 cells were co-transfected by the calcium phosphate precipitate method by two pairs of vectors: pSV2-neo carrying the resistance to the selective agent G-418 and one of the two following vectors expressing the EPO cDNA from the EF1 promoter: pLW24 or p24-MAR. pLW24 had no SAR element, while p24-MAR had the 5'apo B SAR element (Rh10) upstream of the EF 1 promoter region and the 60 bp-deleted 3'apoB SAR element (Rh32) downstream of the EPO cDNA.

G-418 was added to the medium to select cells transfected with pSV2-neo. At least 80% of these transfectants were expected to have been co-transfected with the EPO vector.

The following protocol was used for transfection with the Mammalian Transfection Kit by Stratagene (Catalog #200285). On day-1 100 mm culture dishes were inoculated with exponentially growing mammalian cells at a concentration of 5×10⁴ cells per ml in 10 ml. The cells were grown overnight at 37° C. with the appropriate level of CO₂ and in appropriate medium. For CHO-K1 cells Ham's F12 complete medium with 10% fetal calf serum (FCS) was used and incubation was carried out with 5% CO₂. The cells were approximately 10-20% confluent on day zero.

The optimal amount of DNA to be used for transfection varied depending on the cell type being used for transfection. Usually, 10-30 μg of plasmid DNA was used. The plasmid used for selection was generally added at some ratio to the expression vector. For pSV2neo, a ratio of 1:10 to 1:15 was found to be appropriate.

The desired amount of DNA was diluted to 450 μl with double distilled H₂ O. 50 μl of solution 1 (2.5M Ca Cl₂, included in the Stratagene kit) was added slowly and dropwise. 500 μl of Solution 2 (2×BBS, pH 6.95 consists of 50 mM n, n-bis (2-hydroxyethyl)-2-aminoethanesulfonic acid and buffered saline, 280 mM NaCl and 1.5 mM Na₂ HPO₄ !) was added and mixed gently and slowly. It was found to be important to perform these two additions slowly and gently. The mixture was allowed to incubate at room temperature for 10-20 minutes. The precipitate was gently mixed to ensure adequate suspension. The precipitate was added to the culture dropwise while gently swirling the plate to distribute the suspension evenly, followed by incubation for 12-24 hours.

Where spare incubator space was available, it was determined that transfection efficiency could be improved 2-3 times by using lower CO₂ concentrations at this point (2-4% is recommended; 3% seemed to work well with CHO cells). Normal CO₂ concentrations were resumed after removal of precipitate on Day 1.

On day 1 the medium was removed by aspiration and the culture rinsed twice with sterile PBS (Phosphate buffered saline without Ca²⁺, Mg²⁺) or medium without serum. Fresh complete medium was applied (as on Day-1) and the cells incubated under optimal CO₂ concentration for 24 hours.

The cells were split at a ratio ranging from 1:30 to 1:100 into 96 well plates (0.2 ml per well). For CHO-K1 cells, Ham's F12 complete medium with 20% FCS was used at this step. Incubation was carried out at 37° C. with 5% CO₂.

On day 4 the medium was aspirated and selective medium was added. For transfections using CHO-K1cells and pSV2neo as the selective plasmid, Ham's F12 complete medium with 20% FCS+270-400 μg/ml G418 was used.

On day 5 or 6 (preferably day 5) and on day 8, the cultures were refed with selective medium.

On day 10, spent medium was collected for RIA assays and frozen. The spent medium was replaced with selective medium.

From day 11 RIA assays, were performed to determine levels of EPO production in the medium, using undiluted samples. Samples producing high levels of EPO were cloned and subcultured in Ham's F12 complete medium with 10% FCS when they reached confluency.

EPO Production

Levels of EPO production in the medium were determined by RIA as follows.

The following materials and equipment were used in the assay: phosphate RIA buffer: 0.05M NaPO₄ ; 0.2% BSA; 0.02% NaN₃, pH 7.4; Erythropoietin (standards, Boehringer Mannheim, Cat. #1120166, 250 u/ml); ¹²⁵ I-EPO (Amersham Cat. #IM.219); anti-rabbit IgG (whole molecule) developed in goat, whole antiserum (Sigma Cat. #R-5001 (abbrev. Ab2) polyethylene glycol 8000 (BDH Cat. #B80016); normal rabbit serum (abbrev. NRS); Rabbit anti-EPO, polyclonal, 1 mg (abbrev. Ab1) (R&D Systems Cat. #AB-286-NA) and; gamma counter (LKB-Wallac RIAGamma 1272).

The stock concentration of EPO was 250 U/ml. Eight standard concentrations were prepared from a stock dilution of 20 U/ml sufficient for 4.5 ml of each standard or 20 assays in duplicate. 20 U/ml=88 μl @ 250 U/ml +1012 μl dilution buffer. The eight standard concentrations are shown in Table 2. The standards were divided into 450 μl aliquots in microcentrifuge tubes and stored at -20° C. until used.

Antibody 1 (1 mg) was dissolved in 1 ml RIA/DB and stored in 20 μl aliquots in 0.5 ml microcentrifuge tubes at -20° C. until used (each aliquot was sufficient for 100 assay tubes). On the assay date, Ab1 was prepared at a working concentration of 2 μg/ml with dilution buffer (a 1/500 dilution of the stock aliquot) to give a final assay concentration of 0.67 μg/ml in 300 μl when added as 100 μl to all tubes except non-specific binding (NSB) and total counts (TC).

Since all standard and sample binding inhibition % were based on the maximum binding (MB), to avoid the possibility of having a poor reference duplicate, the MB was determined in quadruplicate.

The ¹²⁵ I-EPO was diluted with 4.5 ml of dilution buffer and divided into 25×0.2 ml aliquots in 500 μl microcentrifuge tubes. A 5 μl sample was added to 50 μl of dilution buffer in an 11×75 mm tube and counted for 1 min. in the RIAGamma using program 2. The corrected CPM usually ranged between 4500-6000 CPM/μl. The tracer aliquots were stored, with lead shielding, at -20° C. until used.

Table 3 lists the assay setup and addition of reagents. The reagents were added and incubated in the following order: A) dilution buffer and NRS @ 1/33.3 were added to the appropriate tubes 3-8; B) EPO standards and sample dilutions were added to the appropriate tubes; C) antibody 1 was added to all tubes except 1-4 and; all tubes were vortexed and incubated at room temperature for 4h. ¹²⁵ I-EPO @ 6000 CPM/100 μl was added to all tubes. As the tracer activity decreases over time, the maximum binding % decreases resulting in a loss of sensitivity and accuracy. Therefore, we used 6000 CPM total counts during the first week of a new batch and increased by 1000 CPM per week thereafter.

All tubes (except TC's) were vortexed and incubated overnight (18-20 hours) @ 40° C. Ab 2 and NRS (1/62.5) was added to all tubes except TC's. All tubes (except TC's) were vortexed and incubated at room temperature for 2 hours. 1.5 ml of 3.8% PEG 8000 (w/v in dilution buffer) was added to all tubes (except TC's) resulting in a final PEG concentration of 3%. All tubes (except TC's) were vortexed and incubated for 10 minutes at room temperature. All tubes were centrifuged (except TC's) at 1500×g and 4° C. for 20 minutes (1500×g=2800 RPM when using the IEC Centra-8R with the Cat. #5737 12×75 mm tube adapters). The supernants were removed by aspiration and the tubes containing the pellets were counted in the gamma counter.

The standard curve was plotted using linear regression of logit (B/Bo) vs log concentration where B=CPM bound and, Bo=maximum CPM bound (reference binding of Ab 1 without inhibitor). The regression line y=C0+C1(x) where, C0=y intercept, C1=slope, x=Log (Concentration), y=Log (R/(1-R)) and, R=B/Bo.

Interference of culture medium was tested by the addition of up to 95 μl of a possible 100 μl sample volume of Ham's F-12 containing 10% FCS. No effect on binding was observed. Recovery of EPO at 100, 300, and 600 mU/ml was 93.85, 100.41, and 96.33% respectively.

Screening was performed as follows. The assay was performed in one day for screening samples by using the following modifications to the above-noted method. Standards and sample dilutions were incubated with Ab1 for 1 hour at 37° C. instead of 4 hours at room temperature. ¹²⁵ I-EPO was incubated with all tubes for 1 hour at 37° C. instead of overnight at 4° C. Antibody 2 and NRS are incubated for 1 hour at 37° C. instead of 2 hours at room temperature. The remaining procedures were as described above and the results are given below.

The first transfection series was performed with the following target vectors: PLW24 (EF1 promoter, EPO_(Long)) referred to as EPO-1 or; p24MAR-1 (EF1 promoter, EPO_(Long), 5'apoB & 3' 60 bp-deleted apoB SAR elements) referred to as EPO-1*. The selection plasmid was pSV2neo. The target:selection plasmid ratio was 5:1 (30 μg:6 μg).

One sample was picked up randomly from each transfection and was cloned by the dilution method. EPO-1-0-1 was cloned from the EPO-1 transfection and EPO-1-0-4* from the EPO-1* transfection (* indicates the presence of SAR elements in the target vector).

After the first round of cloning, the two EPO-1 clones and four EPO-1* clones expressing the highest levels of EPO were selected and expanded. Levels of EPO production in the medium, determined by the RIA assays were as follows: EPO-1-1-5: 8 u/10⁶ cells/day; EPO-1-1-6:9 u/10⁶ cells/day; EPO-1-1-7*: 41 u/10⁶ cells/day; EPO-1-1-8*: 30 u/10⁶ cells/day; EPO-1-1-13*: 125 u/10⁶ cells/day and; EPO-1-1-14*: 81 u/10⁶ cells/day.

After a second round of cloning, levels of EPO expression were as follows: EPO-1-2-22: 5 u/10⁶ cells/day; EPO-1-2-23: 7 u/10⁶ cells/day; EPO-1-2-26: 13 u/10⁶ cells/day; EPO-1-2-27: 19 u/10⁶ cells/day; EPO-1-2-15*: 13 u/10⁶ cells/day; EPO-1-2-16*: 20 u/10⁶ cells/day and; EPO-1-2-17*: 105 u/10⁶ cells/day.

The second transfection series was performed with the same target and selection vectors as the first transfection series. The target plasmid:selection plasmid ratio was 12:1 (30 μg:2.5 μg).

At day 10 after transfection, EPO-2-0-11 (producing 0.8 u/ml EPO) from EPO-2 transfection (target plasmid has no SAR elements) and EPO2-0-9* (producing 0.6 u/ml) from EPO-2* transfection (target plasmid with SAR elements) were selected for cloning. 21 days after cloning, the levels of EPO production in the medium for EPO-2-0-11 were as follows: 36/48 samples had <160 u/ml; 11/48 samples had 160-800 u/ml; and 1/48 samples had 800 u/ml. Levels of EPO production for EPO-2-0-9* were as follows: 47/48 samples had 1,000-4,000 u/ml and; 1/48 samples had <800 u/ml.

Two of the EPO-2 clones and three of the EPO-2* clones (expressing the highest levels of EPO per cell cluster) were expanded, and the levels of expression were as follows: EPO-2-1-24 (514 u/ml 21 days after cloning) and 109 u/10⁶ cells/day after expansion; EPO2-1-25 (800 u/ml 21 days after cloning) and 182 u/10⁶ cells/day after expansion; EPO-2-1-18* (1,962 u/ml 21 days after cloning) and 185 u/10⁶ cells/day after expansion; EPO-2-1-19* (1,682 u/ml 21 days after cloning) and 1,306 u/10⁶ cells/day after expansion and; EPO-2-1-21* (1,777 u/ml 21 days after cloning) and 332 u/10⁶ cells/day after expansion.

EPO-2-1-19* was found to maintain its levels of EPO production while submitted to successive freezing-revival cycles as follows: 962 and 1,038 u/10⁶ cells/day after the first cycle; 1,323 and 1,264 u/10⁶ cells/day (between days 3 and 4) after the second cycle and; 1,188 u/10⁶ cells/day (between days 3 and 4) after the third cycle.

EPO-2-1-19* was submitted to a second round of cloning. The clones producing the highest levels of EPO produced between 1,500 and 1,700 u/10⁶ cells/day (between days 3 and 4). The EPO-2-1-19* cell line has remained stable and expressed constant levels of EPO for about eight months.

                  TABLE 1     ______________________________________     Assembly of expression vectors     EF1       CMV        EPO        5' SAR                                           3' SAR     promoter  promoter   sequence   element                                           element     ______________________________________     pLW24 Rh49               pLW25 Rh216                          cDNA.sub.long                                     --    --     p24MAR-1  p25MAR-1   cDNA.sub.long                                     Rh10  Rh32     Rh163     Rh101     pAP142 Rh223               pAP140 Rh233                          cDNA.sub.long                                     Rh32  Rh32     pAP59 Rh183               pAP67 Rh209                          genomic    --    --     pAP123 Rh211               pAP127 Rh201                          genomlc    Rh32  Rh32     pAP132 Rh221               pAP134 Rh222                          genomic    Rh10  Rh32     ______________________________________

                  TABLE 2     ______________________________________                            Dilution                                    Standard               20 U/ml Stock                            Buffer  Concentration     Standard No.               (μl)      (μl) (mU/ml)     ______________________________________     1          4.5         4495.5   20     2          9.0         4491.0   40     3          18.0        4482.0   80     4          36.0        4464.0  160     5          67.5        4432.5  300     6         135.0        4365.0  600     7         270.0        4230.0  1,200     8         450.0        4050.0  2,000     ______________________________________

                                      TABLE 3     __________________________________________________________________________                                         I-EPO                   Dilution                        NRS @                             EPO   Ab1 @ 6000 CPM                                              Ab2 @ 1/5                                                    NRS @     Tube #  Code  Buffer (μl)                        1/33.3 (μl)                             Standard (μl)                                   2 μg/ml (μl)                                         (μl)                                              (μl)                                                    1/62.5 (μl)     __________________________________________________________________________     1-2     TC    0    0     0     0    100   0     0     34      NSB   100  100   0     0    100  50    50     5-8     MB    100  0     0    100   100  50    50     Standard     Curve      9-10    20 mU/ml                   0    0    100   100   100  50    50     11-12    40 mU/ml                   0    0    100   100   100  50    50     13-14    80 mU/ml                   0    0    100   100   100  50    50     15-16    160 mU/ml                   0    0    100   100   100  50    50     17-18    300 mU/ml                   0    0    100   100   100  50    50     19-20    600 mU/ml                   0    0    100   100   100  50    50     21-22   1200 mU/ml                   0    0    100   100   100  50    50     23-24   2000 mU/ml                   0    0    100   100   100  50    50     Inter/Intra-assay     Quality Controls     25-26    100 mU/ml                   0    0    100   100   100  50    50     27-28    400 mU/ml                   0    0    100   100   100  50    50     29-30    800 mU/ml                   0    0    100   100   100  50    50     Unknowns     31-32   Sample 1                   100 μl of                        0     0    100   100  50    50                   Sample                   Dilution     __________________________________________________________________________

    __________________________________________________________________________     SEQUENCE LISTING     (1) GENERAL INFORMATION:     (iii) NUMBER OF SEQUENCES: 37     (2) INFORMATION FOR SEQ ID NO:1:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 51 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO1     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:     AGCTTGCCCGGGATGAGGGCCACCGGTGTGGTCACCCGGCGCGCCCCAGGT51     (2) INFORMATION FOR SEQ ID NO:2:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 44 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO2     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:     CGCTGAGGGACCCCGGCCAGGCGCGGAGATGGGGGTGCACGAAT44     (2) INFORMATION FOR SEQ ID NO:3:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 51 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO3     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:     GTCCTGCCTGGCTGTGGCTTCTCCTGTCCCTGCTGTCGCTCCCTCTGGGCC51     (2) INFORMATION FOR SEQ ID NO:4:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 59 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO4     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:4:     TCCCAGTCCTGGGCGCCCCACCACGCCTCATCTGTGACAGCCGAGTCCTGGAGAGGTAC59     (2) INFORMATION FOR SEQ ID NO:5:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 56 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO5     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5:     CTCTTGGAGGCCAAGGAGGCCGAGAATATCACGACGGGCTGTGCTGAACATTGCAG56     (2) INFORMATION FOR SEQ ID NO:6:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 58 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO6     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:6:     CTTGAATGAGAATATCACTGTCCCAGACACCAAAGTTAATTTCTATGCCTGGAAGAGG58     (2) INFORMATION FOR SEQ ID NO:7:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 55 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO7     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:7:     ATGGAGGTCGGGCAGCAGGCCGTAGAAGTCTGGCAGGGCCTGGCCCTGCTGTCGG55     (2) INFORMATION FOR SEQ ID NO:8:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 61 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO8     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:8:     AAGCTGTCCTGCGGGGCCAGGCCCTGTTGGTCAACTCTTCCCAGCCGTGGGAGCCCCTGC60     A61     (2) INFORMATION FOR SEQ ID NO:9:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 54 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO9     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:9:     GCTGCATGTGGATAAAGCCGTCAGTGGCCTTCGCAGCCTCACCACTCTGCTTCG54     (2) INFORMATION FOR SEQ ID NO:10:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 51 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO10     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:10:     GGCTCTGGGAGCCCAGAAGGAAGCCATCTCCCCTCCAGATGCGGCCTCAGC51     (2) INFORMATION FOR SEQ ID NO:11:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 51 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO11     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:11:     TGCTCCACTCCGAACAATCACTGCTGACACTTTCCGCAAACTCTTCCGAGT51     (2) INFORMATION FOR SEQ ID NO:12:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 47 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO12     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:12:     CTACTCCAATTTCCTCCGGGGAAAGCTGAAGCTGTACACAGGGGAGG47     (2) INFORMATION FOR SEQ ID NO:13:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 48 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO13     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:13:     CCTGCAGGACAGGGGACAGATGACCAGGTGTGTCGACCTGGGCATATC48     (2) INFORMATION FOR SEQ ID NO:14:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 48 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO13b     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:14:     CCTGCAGGACAGGGGACAGATGACCAGGTGTGTCCACCTGGGCATATC48     (2) INFORMATION FOR SEQ ID NO:15:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 50 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO15     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:15:     CACCACCTCCCTCACCAATATTGCTTGTGCCACACCCTCCCCCGCCACTC50     (2) INFORMATION FOR SEQ ID NO:16:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 52 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO15     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:16:     CTGAACCCCGTCGAGGGGCTCTCAGCTCAGCGCCAGCCTGTCCCATGGACCA52     (2) INFORMATION FOR SEQ ID NO:17:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 55 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO1 alpha     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:17:     CCTCAGCGACCTGGGGCGCGCCGGGTGACCACACCGGTGGCCCTCATCCCGGGCA55     (2) INFORMATION FOR SEQ ID NO:18:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 44 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO2 alpha     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:18:     GGCAGGACATTCGTGCACCCCCATCTCCGCGCCTGGCCGGGGTC44     (2) INFORMATION FOR SEQ ID NO:19:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 52 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO3 alpha     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:19:     GGACTGGGAGGCCCAGAGGGAGCGACAGCAGGGACAGGAGAAGCCACAGCCA52     (2) INFORMATION FOR SEQ ID NO:20:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 46 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO4 alpha     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:20:     CTCTCCAGGACTCGGCTGTCACAGATGAGGCGTGGTGGGGCGCCCA46     (2) INFORMATION FOR SEQ ID NO:21:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 52 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO5 alpha     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:21:     TTCAGCACAGCCCGTCGTGATATTCTCGGCCTCCTTGGCCTCCAAGAGGTAC52     (2) INFORMATION FOR SEQ ID NO:22:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 58 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO6A     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:22:     AGGCATAGAAATTAACTTTGGTGTCTGGGACAGTGATATTCTCATTCAAGCTGCAATG58     (2) INFORMATION FOR SEQ ID NO:23:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 55 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO7 alpha     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:23:     AGGGCCAGGCCCTGCCAGACTTCTACGGCCTGCTGCCCGACCTCCATCCTCTTCC55     (2) INFORMATION FOR SEQ ID NO:24:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 65 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO8 alpha     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:24:     GGGGCTCCCACGGCTGGGAAGAGTTGACCAACAGGGCCTGGCCCCGCAGGACAGCTTCCG60     ACAGC65     (2) INFORMATION FOR SEQ ID NO:25:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 50 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO9 alpha     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:25:     AGTGGTGAGGCTGCGAAGGCCACTGACGGCTTTATCCACATGCAGCTGCA50     (2) INFORMATION FOR SEQ ID NO:26:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 51 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO10 alpha     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:26:     CGCATCTGGAGGGGAGATGGCTTCCTTCTGGGCTCCCAGAGCCCGAAGCAG51     (2) INFORMATION FOR SEQ ID NO:27:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 61 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO11 alpha     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:27:     AGACTCGGAAGAGTTTGCGGAAAGTGTCAGCAGTGATTGTTCGGAGTGGAGCAGCTGAGG60     C61     (2) INFORMATION FOR SEQ ID NO:28:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 53 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO 12 alpha     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:28:     CCTGCAGGCCTCCCCTGTGTACAGCTTCAGCTTTCCCCGGAGGAAATTGGAGT53     (2) INFORMATION FOR SEQ ID NO:29:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 47 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO13 alpha     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:29:     GGTGGTGGATATGCCCAGGTCGACACACCTGGTCATCTGTCCCCTGT47     (2) INFORMATION FOR SEQ ID NO:30:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 47 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO13b alpha     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:30:     GGTGGTGGATATGCCCAGGTGGACACACCTGGTCATCTGTCCCCTGT47     (2) INFORMATION FOR SEQ ID NO:31:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 51 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO14 alpha     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:31:     GGGTTCAGGAGTGGCGGGGGAGGGTGTGGCACAAGCAATATTGGTGAGGGA51     (2) INFORMATION FOR SEQ ID NO:32:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 48 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPO15 alpha     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:32:     AGCTTGGTCCATGGGACAGGCTGGCGCTGAGCTGAGAGCCCCTCGACG48     (2) INFORMATION FOR SEQ ID NO:33:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 3602 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: DNA (genomic)     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (ix) FEATURE:     (A) NAME/KEY: CDS     (B) LOCATION: join(625..637, 1201..1346, 1605..1691, 2303..     2482, 2617..2772)     (ix) FEATURE:     (A) NAME/KEY: mRNA     (B) LOCATION: join(625..637, 1201..1346, 1605..1691, 2303..     2482, 2617..2772)     (ix) FEATURE:     (A) NAME/KEY: mat_peptide     (B) LOCATION: join(1269..1346, 1605..1691, 2303..2482, 2617     ..2769)     (ix) FEATURE:     (A) NAME/KEY: prim_transcript     (B) LOCATION: join(625..3337)     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:33:     AAGCTTCTGGGCTTCCAGACCCAGCTACTTTGCGGAACTCAGCAACCCAGGCATCTCTGA60     GTCTCCGCCCAAGACCGGGATGCCCCCCAGGGGAGGTGTCCGGGAGCCCAGCCTTTCCCA120     GATAGCACGCTCCGCCAGTCCCAAGGGTGCGCAACCGGCTGCACTCCCCTCCCGCGACCC180     AGGGCCCGGGAGCAGCCCCCATGACCCACACGCACGTCTGCAGCAGCCCCGCTCACGCCC240     CGGCGAGCCTCAACCCAGGCGTCCTGCCCCTGCTCTGACCCCGGGTGGCCCCTACCCCTG300     GCGACCCCTCACGCACACAGCCTCTCCCCCACCCCCACCCGCGCACGCACACATGCAGAT360     AACAGCCCCGACCCCCGGCCAGAGCCGCAGAGTCCCTGGGCCACCCCGGCCGCTCGCTGC420     GCTGCGCCGCACCGCGCTGTCCTCCCGGAGCCGGACCGGGGCCACCGCGCCCGCTCTGCT480     CCGACACCGCGCCCCCTGGACAGCCGCCCTCTCCTCTAGGCCCGTGGGGCTGGCCCTGCA540     CCGCCGAGCTTCCCGGGATGAGGGCCCCCGGTGTGGTCACCCGGCGCGCCCCAGGTCGCT600     GAGGGACCCCGGCCAGGCGCGGAGATGGGGGTGCACGGTGAGTACTC647     MetGlyValHis     27-25     GCGGGCTGGGCGCTCCCGCCGCCCGGGTCCCTGTTTGAGCGGGGATTTAGCGCCCCGGCT707     ATTGGCCAGGAGGTGGCTGGGTTCAAGGACCGGCGACTTGTCAAGGACCCCGGAAGGGGG767     AGGGGGGTGGGGCAGCCTCCACGTGCCAGCGGGGACTTGGGGGAGTCCTTGGGGATGGCA827     AAAACCTGACCTGTGAAGGGGACACAGTTTGGGGGTTGAGGGGAAGAAGGTTTGGGGGTT887     CTGCTGTGCCAGTGGAGAGGAAGCTGATAAGCTGATAACCTGGGCGCTGGAGCCACCACT947     TATCTGCCAGAGGGGAAGCCTCTGTCACACCAGGATTGAAGTTTGGCCGGAGAAGTGGAT1007     GCTGGTAGCTGGGGGTGGGGTGTGCACACGGCAGCAGGATTGAATGAAGGCCAGGGAGGC1067     AGCACCTGAGTGCTTGCATGGTTGGGGACAGGAAGGACGAGCTGGGGCAGAGACGTGGGG1127     ATGAAGGAAGCTGTCCTTCCACAGCCACCCTTCTCCCTCCCCGCCTGACTCTCAGCCTGG1187     CTATCTGTTCTAGAATGTCCTGCCTGGCTGTGGCTTCTCCTGTCCCTG1235     GluCysProAlaTrpLeuTrpLeuLeuLeuSerLeu     22-20-15     CTGTCGCTCCCTCTGGGCCTCCCAGTCCTGGGCGCCCCACCACGCCTC1283     LeuSerLeuProLeuGlyLeuProValLeuGlyAlaProProArgLeu     10- 515     ATCTGTGACAGCCGAGTCCTGGAGAGGTACCTCTTGGAGGCCAAGGAG1331     IleCysAspSerArgValLeuGluArgTyrLeuLeuGluAlaLysGlu     101520     GCCGAGAATATCACGGTGAGACCCCTTCCCCAGCACATTCCACAGAACTCACGCT1386     AlaGluAsnIleThr     25     CAGGGCTTCAGGGAACTCCTCCCAGATCCAGGAACCTGGCACTTGGTTTGGGGTGGAGTT1446     GGGAAGCTAGACACTGCCCCCCTACATAAGAATAAGTCTGGTGGCCCCAAACCATACCTG1506     GAAACTAGGCAAGGAGCAAAGCCAGCAGATCCTACGGCCTGTGGGCCAGGGCCAGAGCCT1566     TCAGGGACCCTTGACTCCCCGGGCTGTGTGCATTTCAGACGGGCTGTGCTGAA1619     ThrGlyCysAlaGlu     30     CACTGCAGCTTGAATGAGAATATCACTGTCCCAGACACCAAAGTTAAT1667     HisCysSerLeuAsnGluAsnIleThrValProAspThrLysValAsn     354045     TTCTATGCCTGGAAGAGGATGGAGGTGAGTTCCTTTTTTTTTTTTTTTCCTTTC1721     PheTyrAlaTrpLysArgMetGlu     5055     TTTTGGAGAATCTCATTTGCGAGCCTGATTTTGGATGAAAGGGAGAATGATCGGGGGAAA1781     GGTAAAATGGAGCAGCAGAGATGAGGCTGCCTGGGCGCAGAGGCTCACGTCTATAATCCC1841     AGGCTGAGATGGCCGAGATGGGAGAATTGCTTGAGCCCTGGAGTTTCAGACCAACCTAGG1901     CAGCATAGTGAGATCCCCCATCTCTACAAACATTTAAAAAAATTAGTCAGGTGAAGTGGT1961     GCATGGTGGTAGTCCCAGATATTTGGAAGGCTGAGGCGGGAGGATCGCTTGAGCCCAGGA2021     ATTTGAGGCTGCAGTGAGCTGTGATCACACCACTGCACTCCAGCCTCAGTGACAGAGTGA2081     GGCCCTGTCTCAAAAAAGAAAAGAAAAAAGAAAAATAATGAGGGCTGTATGGAATACATT2141     CATTATTCATTCACTCACTCACTCACTCATTCATTCATTCATTCATTCAACAAGTCTTAT2201     TGCATACCTTCTGTTTGCTCAGCTTGGTGCTTGGGGCTGCTGAGGGGCAGGAGGGAGAGG2261     GTGACATGGGTCAGCTGACTCCCAGAGTCCACTCCCTGTAGGTCGGGCAGCAG2314     ValGlyGlnGln     GCCGTAGAAGTCTGGCAGGGCCTGGCCCTGCTGTCGGAAGCTGTCCTG2362     AlaValGluValTrpGlnGlyLeuAlaLeuLeuSerGluAlaValLeu     60657075     CGGGGCCAGGCCCTGTTGGTCAACTCTTCCCAGCCGTGGGAGCCCCTG2410     ArgGlyGlnAlaLeuLeuValAsnSerSerGlnProTrpGluProLeu     808590     CAGCTGCATGTGGATAAAGCCGTCAGTGGCCTTCGCAGCCTCACCACT2458     GlnLeuHisValAspLysAlaValSerGlyLeuArgSerLeuThrThr     95100105     CTGCTTCGGGCTCTGGGAGCCCAGGTGAGTAGGAGCGGACACTTCTGCTTGCCC2512     LeuLeuArgAlaLeuGlyAlaGln     110115     TTTCTGTAAGAAGGGGAGAAGGGTCTTGCTAAGGAGTACAGGAACTGTCCGTATTCCTTC2572     CCTTTCTGTGGCACTGCAGCGACCTCCTGTTTTCTCCTTGGCAGAAGGAAGCCATC2628     LysGluAlaIle     TCCCCTCCAGATGCGGCCTCAGCTGCTCCACTCCGAACAATCACTGCT2676     SerProProAspAlaAlaSerAlaAlaProLeuArgThrIleThrAla     120125130135     GACACTTTCCGCAAACTCTTCCGAGTCTACTCCAATTTCCTCCGGGGA2724     AspThrPheArgLysLeuPheArgValTyrSerAsnPheLeuArgGly     140145150     AAGCTGAAGCTGTACACAGGGGAGGCCTGCAGGACAGGGGACAGA     LysLeuLysLeuTyrThrGlyGluAlaCysArgThrGlyAspArg     155160165     TGACCAGGTG2779     TGTCCACCTGGGCATATCCACCACCTCCCTCACCAACATTGCTTGTGCCACACCCTCCCC2839     CGCCACTCCTGAACCCCGTCGAGGGGCTCTCAGCTCAGCGCCAGCCTGTCCCATGGACAC2899     TCCAGTGCCAGCAATGACATCTCAGGGGCCAGAGGAACTGTCCAGAGAGCAACTCTGAGA2959     TCTAAGGATGTCACAGGGCCAACTTGAGGGCCCAGAGCAGGAAGCATTCAGAGAGCAGCT3019     TTAAACTCAGGGACAGAGCCATGCTGGGAAGACGCCTGAGCTCACTCGGCACCCTGCAAA3079     ATTTGATGCCAGGACACGCTTTGGAGGCGATTTACCTGTTTTCGCACCTACCATCAGGGA3139     CAGGATGACCTGGAGAACTTAGGTGGCAAGCTGTGACTTCTCCAGGTCTCACGGGCATGG3199     GCACTCCCTTGGTGGCAAGAGCCCCCTTGACACCGGGGTGGTGGGAACCATGAAGACAGG3259     ATGGGGGCTGGCCTCTGGCTCTCATGGGGTCCAAGTTTTGTGTATTCTTCAACCTCATTG3319     ACAAGAACTGAAACCACCAATATGACTCTTGGCTTTTCTGTTTTCTGGGAACCTCCAAAT3379     CCCCTGGCTCTGTCCCACTCCTGGCAGCAGTGCAGCAGGTCCAGGTCCGGGAAATGAGGG3439     GTGGAGGGGGCTGGGCCCTACGTGCTGTCTCACACAGCCTGTCTGACCTCTCGACCTACC3499     GGCCTAGGCCACAAGCTCTGCCTACGCTGGTCAATAAGGTGTCTCCATTCAAGGCCTCAC3559     CGCAGTAAGGCAGCTGCCAACCCTGCCCAGGGCAAGGCTGCAG3602     (2) INFORMATION FOR SEQ ID NO:34:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 193 amino acids     (B) TYPE: amino acid     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: protein     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:34:     MetGlyValHisGluCysProAlaTrpLeuTrpLeuLeuLeuSerLeu     27-25-20-15     LeuSerLeuProLeuGlyLeuProValLeuGlyAlaProProArgLeu     10- 515     IleCysAspSerArgValLeuGluArgTyrLeuLeuGluAlaLysGlu     101520     AlaGluAsnIleThrThrGlyCysAlaGluHisCysSerLeuAsnGlu     253035     AsnIleThrValProAspThrLysValAsnPheTyrAlaTrpLysArg     404550     MetGluValGlyGlnGlnAlaValGluValTrpGlnGlyLeuAlaLeu     556065     LeuSerGluAlaValLeuArgGlyGlnAlaLeuLeuValAsnSerSer     70758085     GlnProTrpGluProLeuGlnLeuHisValAspLysAlaValSerGly     9095100     LeuArgSerLeuThrThrLeuLeuArgAlaLeuGlyAlaGlnLysGlu     105110115     AlaIleSerProProAspAlaAlaSerAlaAlaProLeuArgThrIle     120125130     ThrAlaAspThrPheArgLysLeuPheArgValTyrSerAsnPheLeu     135140145     ArgGlyLysLeuLysLeuTyrThrGlyGluAlaCysArgThrGlyAsp     150155160165     Arg     (2) INFORMATION FOR SEQ ID NO:35:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 788 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: EPOlong     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:35:     AGCTTGCCCGGGATGAGGGCCACCGGTGTGGTCACCCGGCGCGCCCCAGGTCGCTGAGGG60     ACCCCGGCCAGGCGCGGAGATGGGGGTGCACGAATGTCCTGCCTGGCTGTGGCTTCTCCT120     GTCCCTGCTGTCGCTCCCTCTGGGCCTCCCAGTCCTGGGCGCCCCACCACGCCTCATCTG180     TGACAGCCGAGTCCTGGAGAGGTACCTCTTGGAGGCCAAGGAGGCCGAGAATATCACGAC240     GGGCTGTGCTGAACATTGCAGCTTGAATGAGAATATCACTGTCCCAGACACCAAAGTTAA300     TTTCTATGCCTGGAAGAGGATGGAGGTCGGGCAGCAGGCCGTAGAAGTCTGGCAGGGCCT360     GGCCCTGCTGTCGGAAGCTGTCCTGCGGGGCCAGGCCCTGTTGGTCAACTCTTCCCAGCC420     GTGGGAGCCCCTGCAGCTGCATGTGGATAAAGCCGTCAGTGGCCTTCGCAGCCTCACCAC480     TCTGCTTCGGGCTCTGGGAGCCCAGAAGGAAGCCATCTCCCCTCCAGATGCGGCCTCAGC540     TGCTCCACTCCGAACAATCACTGCTGACACTTTCCGCAAACTCTTCCGAGTCTACTCCAA600     TTTCCTCCGGGGAAAGCTGAAGCTGTACACAGGGGAGGCCTGCAGGACAGGGGACAGATG660     ACCAGGTGTGTCCACCTGGGCATATCCACCACCTCCCTCACCAATATTGCTTGTGCCACA720     CCCTCCCCCGCCACTCCTGAACCCCGTCGAGGGGCTCTCAGCTCAGCGCCAGCCTGTCCC780     ATGGACCA788     (2) INFORMATION FOR SEQ ID NO:36:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 605 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: Rh 32     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:36:     AAAAAGATGAGGTAATTGTGTTTTTATAATTAAATATTTTATAATTAAAATATTTATAAT60     TAAAATATTTATAATTAAATATTTTATAATTAAAATATTTATAATTAAATATTTTATAAT120     TAAAATATTTATAATTAAATATTTTATAATTAAAATATTTATAATTAAATATTTTATAAT180     TAAAATATTTATAATTAAATATTTTATAATTAAAATATTTATAATTAAATATTTTATAAT240     TAAAATATTTATAATTAAATATTTTATAATTAAAATGTTTATAATTACATATTTTATAAT300     TAAAATGTTTATAATTACATATTTTATAATTAAAATGTTTATAATTACATATTTTATAAT360     TAAAATGTTTATAATTACATATTTTATAATTACATATTTTATAAAGTATTTATAATTACA420     TATTTTATAATTAAAGTATTTATAATTACATATTTTATAATTAAAGTATTTATAATTACA480     TATTTTATAATTCAATATTTTATAAATAGTTAAAAAGACGAGGAAAAAATTAAAAAGACG540     AGGTTATTGATCTCAGGAATTGTATTTGCCAAGTGAGAAGGAAAAAATATTCACAAAGGC600     TTGTA605     (2) INFORMATION FOR SEQ ID NO:37:     (i) SEQUENCE CHARACTERISTICS:     (A) LENGTH: 2529 base pairs     (B) TYPE: nucleic acid     (C) STRANDEDNESS: single     (D) TOPOLOGY: linear     (ii) MOLECULE TYPE: cDNA     (vi) ORIGINAL SOURCE:     (A) ORGANISM: Homo sapiens     (vii) IMMEDIATE SOURCE:     (B) CLONE: Rh 10     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:37:     TCTAGACCCCAGTTTCTCTATAAGATGAGAATATTAGTCACGATTTGGTTTCTAAGATCC60     TGTCTATGTTTGAGACTACAGATACCTGTTGCTACATTTCCCTTCATAGCTCTGAACAAG120     GAGAATTCAGCCCAATTCTCATGGCCTTCTAAACAATCCAGAGTTTCAGTGCCATAAGGT180     ACTACAATTTAGTGTCAAATTAAGTCAAAGGCTTCATTAGCCTGAAAGCTCTGTCCCTGG240     CCTGGGCATGGCAAACTGTATCCCCCACTGACCATCCCCCTGTCTCCCTTCTCCCCAGAG300     ACTCCAGTAGCCTGGCGTCATCACAGGGGCCAGACATATCCAACATGTTCCCAGCTTCCT360     GCCACTTGACTTTCAGTGTGCCTCCCTCTTCAGTTACCCAAATCCTGCCCACCATTCCAG420     AGCCAGTTCAATCTCACCCATCCAGGACCCCCGAGACCCCCATCGTACCACTATAGTCTA480     ACTGTGGTGTAGACCCCACACTGGGCACATTGCGTACGCTCATTATTGGCTGTGACGTCT540     GATTATGCCCTTCTCCTGGTCTGGAAGCTCTCGGAGGTGCTCCATAATACATGAAGAGAA600     GTAGTGCTGGTGTGGGAATAGTGAGGTGTGTTTATCCATCCAGCTATCCGGCACCAGCAC660     TGGTCTCAGCTTTCTGAGGTAACACGTTCTGAGCCTTAGTCTTGAGAGAACATAAAGAAA720     ACTTTTTTTAAAAGTAGTAAAAAGTGGCTGACAAAAGCTGACCAAAAGCCTTCAAAAGAA780     ATGCTAAGTTATATCTAAGAAAGTTTACCCAAGGTCAGGCAAATATGAAACCTAAAGCTA840     GACGTGGGGAAGAACTTCCGGAGAGTTGCAATTCCCTGTGCCCCAGCATCCCCAGGAGGG900     CATGCCCACATCTGATTTAGAAATCTGTGTAAAATGAGTGAAGGTTTCTATTTCTTGGGC960     AGTGTGGGCACAGGTCTTTGGAGAGGTCGATGGCCTCCCATAAAATCCTTCCTGCTTGAT1020     GGTTCTGGATCCTCAGCCACAGCTCCTAATAGCCATGAGGTTTGAGCCCAAAATAATTTA1080     TGTGTTTGTTTTTTCAGCCCCAAAATTTCCATAGAATCAAAGTAGTCAGAGCTGAATGGG1140     GCTAAGAGACCGTCCATTCCTGTCTTCTCATCACAGATGAGGGACTGCCACCCAGAGCCG1200     TAGAAACTGTCCCATGGCCCCAGTTCCCAGACCCTTCCTCTCTCCTACAGCTCCAAGTTC1260     ACTGTGCATTCTAAATGAAGATGTAAACATAGGCAGCAACACTCAAGAGTAAAAATGAAG1320     TGTGCATATGAAAGAAACCTATTCACATGGACCATATTACATTATAATCACAGTGTTTAC1380     TGCTTGACTACCATCTGCCTGGGCTAGCAAGGGTGTCAGTGAGGAAGAGAGGACAAGGGG1440     TACCAATCTGTGAACTACACATGGTTCTTGCTCTCCCAGCTTCTCTCTCCCATTGGCAAG1500     GCAACAGGTAAACACATGAAAAATCAAATAATGCTATAAGAGAAAAATGTATTCAGGACA1560     ACAACAGGTTTGTATGAAGGCCTTTCATCATCGTTGTCCTACCTAGAAACTGAATGACAG1620     GGAATCAGAGTCACAAGCTATGAAGTCTAACTGGGCTGGTCCCAGAGAAAGATTCAGTGC1680     AGTAGGTGGGGCTGCAGCCAGCCCTGGGTGGGTGGAAGGATGACATCCACATAGGCAAGA1740     GGGTGATAATTCACTTGCGCAGCTCCTCACTGCACATTGAACCCTGCTGACTTCTGGCTT1800     CTCTCCCGGGAGGAACTGCGACTCAACATTCTGACCTTATCTCTTGGGTAGCAGAATGAT1860     GGAGAAGGAAAGTTTCTTTTTGCTTCTCGCAGGGGTTAATCATCCATCTGGAATGCCTAC1920     ATTTGGTTGACAATGGCTCACCCTATCATCTTCCTCCTGAACCATTCACCTAAATGTGCC1980     ATTTCTTTCCTGATAGTTCTCATTTGTGTGTGTGTGTGTGTGTGTGTGTGTGCACGTGCT2040     CACACATGCATGCTGTCACTGGGTAAACAGGCCACCCTGGGCACAGTTCCATCTACAATG2100     TTTGAAGTTTACTTTCCAGCTTCTGGGCATCATTTGCAATTATAATGCTGTCACAGGCAG2160     AAACGAGATAGGCTAATTAATCGTTGTCAATACTGATCCCTATTTGCCAGATGAGATTTT2220     GGAGCAGCATGGCTGGGAATAATTGGTATAGACTGTATTTCCTTGCTTTATGTCACTGGA2280     AATATTTATTTAAGCATCACGGTCGCTATGCATAAATATCCTGGAAAATGGGGTATAGCT2340     GAATGGTGCAGATTCATTCATTCATATTCAGCAAATTATGTTCTAAGCACCTACTTCAGT2400     ACGTGAACAGCACTAAACTCAGAATATTGGTCTGCTGGGGTCCTTTATTAGCTTCCATGA2460     TTCCCTGAACTTGGCCAAGACCCTTCTGGTCGGCTGCAGATAGGCACAATGGATAGTTTT2520     GCTTCTAGA2529     __________________________________________________________________________ 

I claim:
 1. A recombinant DNA molecule adapted for expression of erythropoietin, comprising a nucleic acid molecule encoding mammalian erythropoietin, an expression control sequence operatively linked thereto and at least one human apolipoprotein B SAR element.
 2. A recombinant DNA molecule as claimed in claim 1 wherein the nucleic acid molecule encodes human erythropoietin.
 3. A recombinant DNA molecule as claimed in claim 2 wherein the nucleic acid molecule encodes erythropoietin having the amino acid sequence shown in SEQ ID NO
 34. 4. A recombinant DNA molecule as claimed in claim 3 wherein the nucleic acid molecule has the sequence as shown in SEQ ID NO.
 35. 5. A recombinant DNA molecule as claimed in claim 1 wherein the SAR element comprises the sequence as shown in SEQ ID NO. 36 or
 37. 6. A recombinant DNA molecule as claimed in claim 1 wherein the nucleic acid molecule encoding mammalian erythropoietin and the expression control sequence operatively linked thereto are flanked by SAR elements.
 7. An expression vector comprising a recombinant DNA molecule as claimed in claim
 1. 8. An expression vector comprising a nucleic acid molecule encoding erythropoietin and having the sequence shown in SEQ ID NO.35 under the control of a promoter, flanked by 5' and 3' human apolipoprotein B SAR elements.
 9. An expression vector as claimed in claim 8 wherein the promoter is a human cytomegalovirus IE enhancer and promoter, or an elongation factor-1 alpha promoter.
 10. A mammalian cell transformed with an expression vector as claimed in claim
 7. 11. A mammalian cell as claimed in claim 10 lacking a selectable gene capable of being amplified, said cell being capable of expressing recombinant erythropoietin in vitro at levels of at least about 2,000 u/10⁶ cells in 24 hours.
 12. A method of expressing recombinant mammalian erythropoietin comprising the steps of culturing a mammalian cell as claimed in claim 11 in a suitable medium until sufficient amounts of erythropoietin are produced by the cell and separating the erythropoietin produced.
 13. A method of preparing recombinant erythropoietin comprising transfecting a mammalian cell with an expression vector comprising a recombinant DNA molecule as claimed in claim 1, and culturing the transfected cell in a suitable medium until sufficient amounts of erythropoietin are produced by the cell and separating the erythropoietin produced.
 14. A method as claimed in claim 12 wherein the mammalian cell is further transfected with a selectable marker gene and wherein transfected cells are selected by means of the selectable marker gene.
 15. A method as claimed in claim 14 wherein the selectable marker gene is neo.
 16. A method as claimed in claim 12 comprising the additional step of identifying and selecting cells producing high levels of erythropoietin; subcloning the selected cells; establishing long term cell lines from the selected cells and; culturing the selected cells in a suitable medium until sufficient amounts of erythropoietin are produced by the cell and separating the erythropoietin produced.
 17. A method as claimed in claim 12 wherein erythropoietin is produced at levels of at least 1,500 u/10⁶ cells in 24 hours in the absence of gene amplification. 